Optical system and imaging system incorporating it

ABSTRACT

The invention relates to an optical system that is capable of providing a zoom lens having improved image-formation capability with a reduced number of lenses, and fabricating a slim yet high-performance digital or video camera. The optical system comprises a cemented lens having a cementing surface on its optical axis. Air contact surfaces on the light ray entrance and exit sides of the cemented lens G 2  are aspheric, and at least one cementing surface in the cemented lens G 2  satisfies condition (1). 
 
6.4&lt;|( r/R )|  (1) 
Here r is the axial radius of curvature of the cementing surface, and R is the maximum diameter of the cementing surface.

This application claims benefits of Japanese Application No. 2004-246220filed in Japan on Aug. 26, 2004 and No. 2005-147615 filed in Japan onMay 20, 2005, the contents of which are herein incorporated by thisreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to an optical system and animaging system incorporating it, and more particularly to a zoom lenswell suitable in construction for use on digital or video cameras, inwhich its optical system portion is so elaborated that albeit having ahigh zoom ratio, it can be slimmed down with reduced influences ofdecentration and so little or no performance deteriorations, and animaging system incorporating the same.

There is now a growing demand for slimming down zoom lenses in generaland those for digital cameras in particular. With digital cameras usingsmall-format image pickup devices, in general, lenses may be designed tobe smaller than those used with silver halide cameras. However, lenspart fabrication errors, and errors upon incorporation of lens parts ina lens barrel become relatively large, often incurring performancedeteriorations due to decentration and, hence, resulting in yield drops.Often for slimming down cameras, lenses that form a zoom lens must be asfew as possible, and as many aspheric surfaces as possible must be usedfor correction of aberrations with fewer lenses.

However, such an optical system is susceptible of image-formationcapability drops by reason of relative decentration between asphericlenses due to fabrication errors, and so it is still difficult to offera sensible tradeoff between high-yield mass fabrication andslimming-down.

Reductions in the number of lenses through use of many asphericsurfaces, for instance, are set forth in patent publications 1, 2, 3 and4; in any case, however, the sensitivity to decentration of asphericsurfaces in the second lens group is unacceptably high, failing toreduce the total thickness of each lens group to a sufficient level.

There are also patent publications 5, 6 and 7. However, with the zoomlens of patent publication 5 there are problems such as noticeableperformance deterioration (regarding off-axis aberrations in particular)ascribable to decentration of fabrication errors of individual lenses,and inadequate correction of chromatic aberrations by reason of a smallAbbe constant difference between lenses that forms a cemented lens. Thezoom lenses of patent publications 5 and 6 are less than satisfactory interms of slimming-down, because no aspheric surface is used at all.

Patent Publication 1

JP (A) 1-183616

Patent Publication 2

JP (A) 10-282416

Patent Publication 3

JP (A) 11-95102

Patent Publication 4

JP (A) 11-142734

Patent Publication 5

JP (A) 2004-102211

Patent Publication 6

JP (A) 2002-350726

Patent Publication 7

JP (A) 2004-198855

SUMMARY OF THE INVENTION

According to the first embodiment of the first aspect of the invention,there is provided an optical system comprising a cemented lens having acementing surface on an optical axis of the optical system, wherein aircontact surfaces that are on a light ray entrance side and a light rayexit side of said cemented lens are aspheric and at least one cementingsurface in said cemented lens satisfies condition (1):6.4<|(r/R)|  (1)where r is the radius of curvature of the cementing surface on theoptical axis and R is the maximum diameter of the cementing surface.

According to the second embodiment of the first aspect of the invention,there is provided an optical system comprising, in order from an objectside to an image plane side thereof,

a first lens group having negative refracting power, and

a second lens group having positive refracting power which, uponzooming, is positioned nearer to the image plane side than said firstlens group with a variable spacing therebetween, wherein:

said second lens has only three lenses, a lens located in said secondlens group and nearest to an image plane side thereof and a lens locatedon an object side thereof are provided as a cemented lens cemented at asurface on an optical axis of the optical system, and

a d-line refractive index n₂₃ of said lens nearest to said image planeside and a d-line refractive index n₂₂ Of the lens cemented to theobject side of said lens satisfy condition (2):0.31<|n ₂₂ −n ₂₃|  (2)

According to the third embodiment of the first aspect of the invention,there is provided an optical system comprising, in order from an objectside to an image plane side thereof,

a first lens group having negative refracting power, and a second lensgroup having positive refracting power which, upon zooming, ispositioned nearer to the image plane side than said first lens groupwith a variable spacing therebetween, wherein:

said second lens group has only three lenses, and

a lens located in said second lens group and nearest to an image planeside thereof and a lens located on an object side thereof are providedas a cemented lens cemented at a surface on an optical axis of theoptical system, and

the optical system comprises an aperture stop interposed between an exitsurface in said first lens group and an entrance surface of saidcemented lens, wherein:

a d-line basis Abbe constant ν₂₃ of said lens nearest to the image planeside and a d-line basis Abbe constant n₂₂ of the lens cemented to saidlens satisfy condition (3):40.3<|ν₂₂−ν₂₃|  (3)

According to the first embodiment of the second aspect of the invention,there is provided an optical system comprising, in order from an objectside thereof,

a first lens group of negative refracting power, and

a second lens group of positive refracting power, wherein:

the optical system comprises a cemented lens comprising three or morelenses including at least one negative lens, wherein the cemented lenshas generally positive refracting power, and

the optical system has a zoom ratio of 2 or higher, and satisfiesconditions (11) and (12):|F _(oc) /F _(ci)|<0.95   (11)0.05<D _(co) /D _(ci)<20   (12)where F_(co) is the focal length of the lens located in said cementedlens and nearest to its object side,

F_(ci) is the focal length of the lens located in said cemented lens andnearest to its image plane side,

D_(co) is the axial thickness of the lens located in said cemented lensand nearest to its object side, and

D_(ci) is the axial thickness of the lens located in said cemented lensand nearest to its image plane side.

According to the second embodiment of the second aspect of theinvention, there is provided an optical system comprising, in order froman object side thereof,

a first lens group of negative refracting power, and

a second lens group of positive refracting power, wherein:

the optical system comprises a cemented lens comprising three or morelenses including at least one negative lens, wherein the cemented lenshas generally positive refracting power, and

the optical system has a zoom ratio of 2 or higher, and satisfiescondition (13):10<|R ₁ /r ₁|  (13)where r₁ is the radius of curvature of the surface nearest to the objectside of said cemented lens, and

R₁ is the radius of curvature of the cementing surface located in saidcemented lens and nearest to its object side.

According to the third aspect of the second aspect of the invention,there is provided an optical system comprising, in order from an objectside thereof,

a first lens group of negative refracting power, and

a second lens group of positive refracting power, wherein:

the optical system comprises a cemented lens comprising three or morelenses including at least one negative lens, wherein the cemented lenshas generally positive refracting power and the object-side surface ofsaid cemented lens is convex, and

the optical system has a zoom ratio of 2 or higher, and satisfiescondition (14):0.7<|R ₂ /r ₂|  (14)where r₂ is the radius of curvature of the surface nearest to the imageplane side of said cemented lens, and

R₂ is the radius of curvature of the cementing surface located in saidcemented lens and nearest to its image plane side.

According to the fourth embodiment of the second aspect of theinvention, there is further provided an optical system comprising acemented lens having a cementing surface on an optical axis of theoptical system, wherein lenses that form said cemented lens satisfyconditions (15) and (16):40<ν_(max)−ν_(min)<80   (15)23.7>ν_(min)   (16)where ν_(max) is the maximum of Abbe constants that the lenses in saidcemented lens have, and

ν_(min) is the minimum of Abbe constants that the lenses in saidcemented lens have.

According to the fifth embodiment of the second aspect of the invention,there is provided an optical system comprising a cemented lens having acementing surface on an optical axis, wherein lenses that form saidcemented lens satisfy conditions (15), (16), (17), (18) and (19):40<ν_(max)−ν_(min)<80   (15)23.7>ν_(min)   (16)60<ν_(max)   (17)1.8<n_(dmax)   (18)1.55>n_(dmin)   (19)where ν_(max) is the maximum of Abbe constants that the lenses in saidcemented lens have,ν_(min) is the minimum of Abbe constants that the lenses in saidcemented lens have,

n_(dmax) is the maximum of refractive indices that the lenses in saidcemented lens have, and

n_(dmin) is the minimum of refractive indices that the lenses in saidcemented lens have.

The present invention embraces an imaging system comprising each of suchoptical systems as recited above, and an electronic image pickup devicefor converting an optical image formed through the optical system intoelectric signals.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a), 1(b) and 1(c) are illustrative in lens arrangement sectionof Example 1 of the zoom optical system according to the invention at awide-angle end, an intermediate setting and a telephoto end,respectively, upon focusing on an infinite object point.

FIGS. 2(a), 2(b) and 2(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 2 of the zoom optical system according to the invention.

FIGS. 3(a), 3(b) and 3(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 3 of the zoom optical system according to the invention.

FIGS. 4(a), 4(b) and 4(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 4 of the zoom optical system according to the invention.

FIGS. 5(a), 5(b) and 5(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 5 of the zoom optical system according to the invention.

FIGS. 6(a), 6(b) and 6(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 6 of the zoom optical system according to the invention.

FIGS. 7(a), 7(b) and 7(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 7 of the zoom optical system according to the invention.

FIGS. 8(a), 8(b) and 8(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 8 of the zoom optical system according to the invention.

FIGS. 9(a), 9(b) and 9(c) are views, as in FIGS. 1(a), 1(b) and 1(c), ofExample 9 of the zoom optical system according to the invention.

FIGS. 10(a), 10(b) and 10(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 10 of the zoom optical system according to the invention.

FIGS. 11(a), 11(b) and 11(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 11 of the zoom optical system according to the invention.

FIGS. 12(a), 12(b) and 12(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 12 of the zoom optical system according to the invention.

FIGS. 13(a), 13(b) and 13(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 13 of the zoom optical system according to the invention.

FIGS. 14(a), 14(b) and 14(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 14 of the zoom optical system according to the invention.

FIGS. 15(a), 15(b) and 15(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 15 of the zoom optical system according to the invention.

FIGS. 16(a), 16(b) and 16(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 16 of the zoom optical system according to the invention.

FIGS. 17(a), 17(b) and 17(c) are views, as in FIGS. 1(a), 1(b) and 1(c),of Example 17 of the zoom optical system according to the invention.

FIGS. 18(a), 18(b) and 18(c) are aberration diagrams for Example 1 uponfocusing on an infinite object point.

FIGS. 19(a), 19(b) and 19(c) are aberration diagrams for Example 2 uponfocusing on an infinite object point.

FIGS. 20(a), 20(b) and 20(c) are aberration diagrams for Example 3 uponfocusing on an infinite object point.

FIGS. 21(a), 21(b) and 21(c) are aberration diagrams for Example 4 uponfocusing on an infinite object point.

FIGS. 22(a), 22(b) and 22(c) are aberration diagrams for Example 5 uponfocusing on an infinite object point.

FIGS. 23(a), 23(b) and 23(c) are aberration diagrams for Example 6 uponfocusing on an infinite object point.

FIGS. 24(a), 24(b) and 24(c) are aberration diagrams for Example 7 uponfocusing on an infinite object point.

FIGS. 25(a), 25(b) and 25(c) are aberration diagrams for Example 8 uponfocusing on an infinite object point.

FIGS. 26(a), 26(b) and 26(c) are aberration diagrams for Example 9 uponfocusing on an infinite object point.

FIGS. 27(a), 27(b) and 27(c) are aberration diagrams for Example 10 uponfocusing on an infinite object point.

FIGS. 28(a), 28(b) and 28(c) are aberration diagrams for Example 11 uponfocusing on an infinite object point.

FIGS. 29(a), 29(b) and 29(c) are aberration diagrams for Example 12 uponfocusing on an infinite object point.

FIGS. 30(a), 30(b) and 30(c) are aberration diagrams for Example 13 uponfocusing on an infinite object point.

FIGS. 31(a), 31(b) and 31(c) are aberration diagrams for Example 14 uponfocusing on an infinite object point.

FIGS. 32(a), 32(b) and 32(c) are aberration diagrams for Example 15 uponfocusing on an infinite object point.

FIGS. 33(a), 33(b) and 33(c) are aberration diagrams for Example 16 uponfocusing on an infinite object point.

FIGS. 34(a), 33(b) and 33(c) are aberration diagrams for Example 17 uponfocusing on an infinite object point.

FIG. 35 is a front perspective view illustrative of the outwardappearance of a digital camera that incorporates the inventive zoomoptical system.

FIG. 36 is a rear perspective view of the digital camera of FIG. 35.

FIG. 37 is a sectional view of the digital camera of FIG. 35.

FIG. 38 is a front perspective view of an uncovered personal computerincorporating the inventive zoom optical system in the form of anobjective optical system.

FIG. 39 is a sectional view of a taking optical system in the personalcomputer.

FIG. 40 is a side view of the FIG. 38 state.

FIGS. 41(a) and 41(b) are a front view and a side view of a cellularphone incorporating the inventive zoom optical system in the form of anobjective optical system, and FIG. 41(c) is a side view of a takingoptical system in it.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First of all, possible arrangements of the optical systems according tothe first and second aspects of the invention will be explained. Then,their examples will be given.

The first optical system according to the first aspect of the inventionis characterized by comprising a cemented lens having a cementingsurface on an optical axis, wherein air contact surfaces that are on alight ray entrance side and a light ray exit side of said cemented lensare aspheric and at least one cementing surface in said cemented lenssatisfies condition (1):6.4<|(r/R)|  (1)where r is the radius of curvature of the cementing surface on theoptical axis and R is the maximum diameter of the cementing surface.

The advantage of, and the requirement for, the first optical system setup as recited above is now explained.

When the cemented lens is set up with adjustment of the relativedecentration of aspheric surfaces before and after the cementingsurface, parts other than the adjusted portion have little or noinfluence on performance.

As the radius of curvature of the cementing surface on the optical axisbecomes less than the lower limit of 6.4 to condition (1), the radius ofcurvature of the cementing surface becomes smaller relative to thediameter of the cementing surface. This renders the entrance and exitsurfaces of lenses likely to undergo relative decentration at the timeof cementing, and so complicated decentration aberrations are likely tooccur due to both the entrance and exit surfaces being aspheric.

According to the second embodiment of the first aspect of the invention,the first optical system is further characterized in that said cementedlens comprises a plurality of cementing surfaces.

The advantage of, and the requirement for, the second optical system setup as recited above is now explained.

In this embodiment, the cemented lens is composed of a plurality oflenses. This facilitates correction of chromatic aberrations,astigmatism, field curvature, etc. Provision of a plurality of cementingsurfaces ensures that the lenses are cemented together in such a way asto cancel out the influences of relative decentration. The cemented lenscould be composed of not only three but also four or more lenses.

According to the third embodiment of the first aspect of the invention,the second optical system is further characterized in that the cementedlens is composed of three lenses.

The advantage of, and the requirement for, the third optical system setup as recited above is now explained. To make the total length of theoptical system short while the influences of decentration are kept back,it is desired that the cemented lens be composed of three lenses.

According to the fourth embodiment of the first aspect of the invention,any one of the first to third optical systems is further characterizedin that it is provided as an image-formation optical system, whereinsaid image-formation optical system comprises:

a positive lens group comprising said cemented lens and having positiverefracting power,

a negative lens group of negative refracting power, which, upon zooming,is positioned on the object side of said positive lens group with avariable spacing between them, and

an aperture stop interposed between the exit surface in said negativelens group and the exit surface in said positive lens group.

The advantage of, and the requirement for, the fourth optical system setup as recited above is now explained.

By making the spacing between the positive lens group and the negativelens group variable, it is possible to have an image-formation opticalsystem having zooming functions.

With this embodiment wherein the aperture stop is located near or withinthe positive lens group, the diameter of the second lens group can besmaller than that of other lens group(s). This is favorable forincreasing refracting power.

On the other hand, this positive lens group has a reduced lens diameter,and so increasing refracting power causes the lenses in the positivelens group to have increasing influences on decentration. If thecemented lens according to the invention is used for that positive lensgroup, aberrations can then be well corrected at aspheric surfaces evenwith increased refracting power, simultaneously with reductions in theinfluences of decentration occurring among the lenses.

The fifth optical system of the first aspect of the invention ischaracterized by comprising, in order from its object side to its imageplane side, a first lens group having negative refracting power and asecond lens group having positive refracting power, which, upon zooming,is positioned nearer to the image plane side than the first lens groupwith a variable spacing between them, wherein:

said second lens group has only three lenses,

the lens nearest to the image plane side of said second lens group and alens located on the object side thereof are provided as a cemented lenscemented at a surface on an optical axis, and

the d-line refractive index n₂₃ of said lens nearest to said image planeside and the d-line refractive index n₂₂ of said lens cemented to theobject side of said lens satisfy condition (2):0.31<|n ₂₂ −n ₂₃|  (2)

The advantage of, and the requirement for, the fifth optical system setup as recited above is now explained.

As the second lens group is made up of three lenses, it helps offer abalanced tradeoff between correction of aberrations at the second lensgroup and size reductions.

Incorporation of the cemented lens in the second lens group is favorablefor correction of chromatic aberrations.

With too small a radius of curvature of the cementing surface, on theother hand, there are some considerable influences of decentration atthe time of cementing. Here, if the lenses to be cemented together havea refractive index difference suitable enough to satisfy condition (2),it is then possible to mitigate the influences of decentration at thetime of cementing, because the cementing surface can have a large radiusof curvature while its refracting power is kept intact.

According to the sixth embodiment of the first aspect of the invention,the fifth optical system is further characterized in that said threelenses are a positive lens, a negative lens and a positive lens asviewed in order from its object side, wherein a cementing surface thatis the object-side surface of the positive lens nearest to the imageplane side is a refracting surface of negative refracting power.

The advantage of, and the requirement for, the sixth optical system setup as recited above is now explained.

By allowing the cementing surface of the negative and positive lenses tohave negative refracting power, the principal points of the whole secondlens group are so nearer to the object side that the spacing between theprincipal points of the first lens group of negative refracting powerand those of the second lens group of positive refracting power canbecome narrower at the telephoto end. This works for achieving higherzoom ratios.

The seventh optical system of the first aspect of the invention ischaracterized by comprising, comprising, in order from an object side toan image plane side thereof, a first lens group having negativerefracting power, and a second lens group having positive refractingpower, which, upon zooming, is positioned nearer to the image plane sidethan said first lens group with a variable spacing therebetween,wherein:

said second lens group has only three lenses, and

the lens nearest to the image plane side of said second lens group and alens located on the object side thereof are provided as a cemented lenscemented at a surface on an optical axis, and

the optical system further comprises an aperture stop interposed betweenan exit surface in said first lens group and an entrance surface of saidcemented lens, and

the d-line basis Abbe constant ν₂₃ of said lens nearest to the imageplane side and the d-line basis Abbe constant n₂₂ of the lens cementedto said lens satisfy condition (3):40.3<|ν₂₂−ν₂₃|  (3)

The advantage of, and the requirement for, the seventh optical systemset up as recited above is now explained.

As the second lens group is made up of three lenses, it helps offer abalanced tradeoff between correction of aberrations at the second lensgroup and size reductions.

Incorporation of the cemented lens in the second lens group is favorablefor correction of chromatic aberrations.

Satisfaction of condition (3) by the cemented lens at a position of theimage plane side near to the stop works for correction of longitudinalchromatic aberration and chromatic aberration of magnification.

According to the eighth embodiment of the first aspect of the invention,any one of the 5^(th) to 7^(th) optical systems is further characterizedby satisfying the following conditions (4), (5) and (6).−1.8<f ₁ /f _(w)<−1.2   (4)1.1<f ₂ /f _(w)<1.5   (5)1.7<f _(t) /f _(w)<2.5   (6)Here f₁ is the focal length of the first lens group, f₂ is the focallength of the second lens group, f_(w) is the focal length of the wholeoptical system at the wide-angle end, and f_(t) is the focal length ofthe whole optical system at the telephoto end.

The advantage of, and the requirement for, the eighth optical system setup as recited above is now explained.

Conditions (4) and (5) define the moderate refracting powers of thefirst lens group and the second lens group in terms of focal length atthe wide-angle end while, at the same time, condition (6) defines a zoomratio.

As there are deviations from the lower limit of −1.8 to condition (4)and the upper limit of 1.5 to condition (5), the refracting power ofeach lens group becomes weak, resulting in an increase in the spaceneeded for zooming movement, and in the whole length of the lens systemat the time of taking.

Deviations from the upper limit of −1.2 to condition (4) and the lowerlimit of 1.1 to condition (5) mean that more lenses are needed forcorrection of aberrations at each lens group, ending up with difficultyin size reductions upon receiving them at a collapsible lens mount.

Condition (6) defines the zoom ratio well fit for users' needs and sizereductions.

More preferably,

the lower limit to condition (4) should be set at −1.7,

the upper limit to condition (4) should be set at −1.3,

the lower limit to condition (5) should be set at 1.2, and

the upper limit to condition (5) should be set at 1.4.

According to the ninth embodiment of the invention, any one of the5^(th) to 8^(th) optical systems is further characterized in that atleast half of air contact surfaces are aspheric, and in an asphericshape approximated to the following formula (A), all conicalcoefficients K are at most zero.x=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y¹⁰   (A)Here r is a paraxial radius of curvature, K is a conical coefficient,and A₄, A₆, A₈ and A₁₀ are the 4^(th)-, 6^(th)-, 8^(th) - and10^(th)-order aspheric coefficients.

The advantage of, and the requirement for, the 9^(th) optical system setup as recited above is now explained. If such an arrangement is allowedto satisfy such conditions, coma and field curvature can then becorrected in a well-balanced state.

According to the 10^(th) embodiment of the first aspect of theinvention, any one of the 5^(th) to 9^(th) optical systems is furthercharacterized in that:

said first lens group consists of, in order from its object side, anegative lens and a positive lens, two in all, and

said second lens group consists of, in order from its object side, apositive lens, a negative lens and a positive lens, three in all, and

said optical system further comprises a third lens group consisting ofone positive lens, which is located on an image plane side of saidsecond lens group with a variable spacing between them, and is providedas a three-group zoom lens.

The advantage of, and the requirement for, the 10^(th) optical systemset up as recited above is now explained. Such construction provides alens layout that is favorable for ensuring a given angle of view at thewide-angle end, a reduction in the whole size upon received at acollapsible lens mount, and balanced aberrations.

According to the 11^(th) embodiment of the first embodiment of theinvention, any one of the 5^(th) to 9^(th) optical systems is furthercharacterized in that:

said first lens group consists of, in order from its object side, anegative lens and a positive lens, two in all,

said second lens group consists of, in order from its object side, apositive lens, a negative lens and a positive lens, three in all, and

said optical system is provided as a two-group zoom lens.

The advantage of, and the requirement for, the 11^(th) optical systemset up as recited above is now explained. Such construction provides alens layout that is favorable for ensuring an angle of view at thewide-angle end, a reduction in the whole size upon received at acollapsible lens mount, and balanced aberrations.

According to the 12^(th) embodiment of the first aspect of theinvention, the 10^(th) or 11^(th) optical system is furthercharacterized in that:

said first lens group consists of, in order from its object side, anegative lens in which the absolute value of the radius of curvature ofits image-side surface is smaller than the absolute value of the radiusof curvature of its object-side surface and a positive meniscus lensconcave on its image side, two in all, and

said second lens group consists of, in order from its object side, apositive lens in which the absolute value of the radius of curvature ofits object-side surface is smaller than the absolute value of the radiusof curvature of its image-side surface, a negative lens in which theabsolute value of the radius of curvature of its image-side surface issmaller than the absolute value of the radius of curvature of itsobject-side surface and a positive lens in which the absolute value ofthe radius of curvature of its object-side surface is smaller than theabsolute value of the radius of curvature of its image-side surface,three in all.

The advantage of, and the requirement for, the 12^(th) optical systemset up as recited above is now explained. Such a lens arrangement worksfor making well-balanced correction of axial aberrations and off-axisaberrations, albeit being composed of fewer lenses. If the principalpoints of the second lens group are located nearer to the first lensgroup, it is then easier to make the focal length of the optical systemon the telephoto end side longer in spite of its small-format size.

According to the 13^(th) embodiment of the first aspect of theinvention, the 12^(th) optical system is further characterized in thatthe axial spacing between the negative lens and the positive lens insaid first lens group is 1.4 mm to 1.6 mm inclusive.

The advantage of, and the requirement for, the 13^(th) optical systemset up as recited above is now explained. This requirement is acondition for locating the principal points of the first lens groupnearer to the object side while, at the same time, diminishing lens sizeto a suitable level.

According to the 14^(th) embodiment of the first aspect of theinvention, any one of the 5^(th) to 13^(th) optical systems is furthercharacterized in that the three lenses in said second lens groups areprovided in the form of a cemented triplet lens.

The advantage of, and the requirement for, the 14^(th) optical systemset up as recited above is now explained. Such an arrangement works forcorrecting aberrations, reducing the size of the second lens group, anddiminishing the influences of decentration.

According to the 15^(th) embodiment of the first aspect of theinvention, the 14^(th) optical system is further characterized in thatthe axial thickness of said cemented triplet lens is up to 6 mm.

The advantage of, and the requirement for, the 15^(th) optical systemset up as recited above is now explained. The cemented triplet lenslocated in the second lens group is favorable for slimming down the lenssystem. Therefore, if the thickness of the cemented triplet lens in thesecond lens group is reduced down to 6 mm or less, it is possible toreduce the thickness of the optical system upon received at acollapsible lens mount.

According to the 16^(th) embodiment of the first aspect of theinvention, the 15^(th) optical system is further characterized in thatthe axial thickness of said cemented triplet lens is up to 5.5 mm.

The advantage of, and the requirement for, the 16^(th) optical systemset up as recited above is now explained. Satisfaction of thisrequirement allows the thickness of the optical system upon received ata collapsible lens mount to be much more reduced.

According to the 17^(th) embodiment of the first aspect of theinvention, any one of the 14^(th) to 16^(th) optical systems is furthercharacterized in that an aperture stop is located right before theobject side of said cemented triplet lens, wherein the ratio of thethickness of said cemented triplet lens to the maximum diameter of saidaperture stop is at least 1.4.

The advantage of, and the requirement for, the 17^(th) optical systemset up as recited above is now explained.

Such an arrangement ensures that one reflecting surface of the cementedlens is nearer to, and another is farther away from, the aperture stop,so that correction of aberrations occurring at the second lens group ismore easily achievable. A suitable spacing between adjacent surfacesmakes adjustment of principal points, lens fabrication or the likeeasier.

According to the 18^(th) embodiment of the first aspect of theinvention, there is provided an imaging system, characterized bycomprising any one of the 5^(th) to 9^(th) optical systems and furtherincluding an electronic image pickup device for converting an opticalimage formed through said optical system into electric signals.

The advantage of, and the requirement for, the imaging system set up asrecited above is now explained.

The optical system of the invention works for a lens arrangement forpermitting an exit light beam to come close to verticality, and so it isapplicable to an imaging system using an electronic image pickup device.

According to the 19^(th) embodiment of the first aspect of theinvention, the first imaging system is further characterized in that theangle of incidence of a chief light ray on the image pickup device inthe maximum image height position at the wide-angle end of the opticalsystem is 15° to less than 30°.

The advantage of, and the requirement for, the second imaging system setup as recited above is now explained. This requirement is a conditionfor offering a balance between influences of the electronic image pickupdevice on oblique incidence capability and size reductions. As the angleof incidence of the chief ray at the wide-angle end becomes smaller thanthe lower limit of 15°, it renders the optical system bulky. As theupper limit of 30° is exceeded, the angle of incidence of light on theelectronic image pickup device becomes large, rendering chromaticshading likely to occur.

According to the 20^(th) embodiment of the first aspect of theinvention, the second imaging system is further characterized in thatthe angle of incidence of a chief light ray on the image pickup devicein the maximum image height position at the wide-angle end of theoptical system is at least 16°.

Referring to the advantage of, and the requirement for, the thirdimaging system set up as recited above, satisfaction of this-requirementis more favorable for size reductions.

According to the first embodiment of the second aspect of the invention,there is provided an optical system, characterized by comprising, inorder from its object side, a first lens group of negative refractingpower and a second lens group of positive refracting power and furthercomprising a cemented lens which has generally positive refracting powerand in which three or more lenses including at least one negative lensare cemented together, wherein:

said optical system has a zoom ratio of at least 2, and satisfiesconditions (11) and (12):|F _(co) /F _(ci)|<0.95   (11)0.05<D _(co) /D _(ci)<20   (12)where F_(co) is the focal length of the lens located in said cementedlens and nearest to its object side,

F_(ci) is the focal length of the lens located in said cemented lens andnearest to its image plane side,

D_(co) is the axial thickness of the lens located in said cemented lensand nearest to its object side, and

D_(ci) is the axial thickness of the lens located in said cemented lensand nearest to its image plane side.

The advantage of, and the requirement for, the first optical system setup as recited above is now explained.

Slim zoom lenses comprising two lens groups, negative and positive, andincluding a cemented lens having positive refracting power andcomprising three or more lenses have already been proposed in the art.In any of those zoom lenses, however, the relative decentration ofsurfaces before and after a cementing surface has some considerableinfluences on performances. For the time being, there is a method ofadjusting performance deterioration due to fabrication errors using onecementing surface; however, it is still impossible to make significantimprovements in both performances at a deteriorated center and aperipheral portion of the screen.

In the invention, the power balance of the entrance- and exit-sidesurfaces that form the cemented lens is properly determined so thatperformance deteriorations at both the center and the periphery ofcementing can be easily mitigated by adjustment of the relative centersof the lenses.

Condition (11) defines the power balance of the entrance- and exit-sidesurfaces that form the cemented lens. As the upper limit of 0.95 isexceeded, it renders it difficult to gain center adjustment for makingimprovements in both central performance and peripheral performance.

As the axial thickness ratio between the lens nearest to the object sideand the lens nearest to the image plane side of the cemented lensdeviates from the range of condition (12) or as there is a deviationfrom the upper limit of 20 or the lower limit of 0.05, it causes thecemented lens itself to become thicker, thwarting size reductions. Italso renders correction of chromatic aberrations difficult. Otherwise,the effect that the cemented lens comprising three or more lenses shouldhave will become slender.

According to the second embodiment of the second aspect of theinvention, there is provided an optical system, characterized bycomprising, in order from its object side, a first lens group ofnegative refracting power and a second lens group of positive refractingpower and further comprising a cemented lens which has generallypositive refracting power and in which three or more lenses including atleast one negative lens are cemented together, wherein:

said optical system has a zoom ratio of at least 2, and is set up insuch a way as to satisfy condition (13):10<|R ₁ /r ₁|  (13)where r₁ is the radius of curvature of the surface nearest to the objectside of said cemented lens, and

R₁ is the radius of curvature of the cementing surface nearest to theobject side of said cemented lens.

The advantage of, and the requirement for, the second optical system setup as recited above is now explained.

Slim zoom lenses comprising two lens groups, negative and positive, andincluding a cemented lens having positive refracting power andcomprising three or more lenses have already been proposed in the art.In any of those zoom lenses, however, the relative decentration ofsurfaces before and after a cementing surface has some considerableinfluences on performances. For the time being, there is a method ofadjusting performance deterioration due to fabrication errors using onecementing surface; however, it is still impossible to make significantimprovements in both performances at a deteriorated center and aperipheral portion of the screen.

In the invention, the radius of curvature, R₁, of the lens cementingsurface nearest to the entrance side of the cemented lens has a valuelarge enough to make changes in the tilts of lens surfaces small uponadjustment of relative lens centers so that the relative lens centerscan be corrected by shifting of the lens surfaces. It is thus possibleto simultaneously keep center and off-axis performance againstdeteriorations from design values.

Condition (13) defines the shape of the lens nearest to the object sideof the cemented lens, and shows that by making the radius of curvatureof the cementing surface R, large, the tilts of the lenses occurringupon adjustment of the relative lens centers are reduced to preventperformance deteriorations.

According to the third embodiment of the second aspect of the invention,there is provided an optical system, characterized by comprising, inorder from its object side, a first lens group of negative refractingpower and a second lens group of positive refracting power and furthercomprising a cemented lens which has generally positive refracting powerand in which three or more lenses including at least one negative lensare cemented together, wherein:

said cemented lens is convex on its object side, and said optical systemhas a zoom ratio of at least 2, and is set up in such a way as tosatisfy condition (14):0.7<|R ₂ /r ₂|  (14)where r₂ is the radius of curvature of the surface nearest to the imageplane side of said cemented lens, and

R₂ is the radius of curvature of the cementing surface nearest to theimage plane side of said cemented lens.

The advantage of, and the requirement for, the thrid optical system ofthe second aspect of the invention set up as recited above is nowexplained.

Slim zoom lenses comprising two lens groups, negative and positive, andincluding a cemented lens having positive refracting power andcomprising three or more lenses have already been proposed in the art.In any of those zoom lenses, however, the relative decentration ofsurfaces before and after a cementing surface has some considerableinfluences on performances. For the time being, there is a method ofadjusting performance deterioration due to fabrication errors using onecementing surface; however, it is still impossible to make significantimprovements in both performances at a deteriorated center and aperipheral portion of the screen.

In the invention, the lens cementing surface R₂ nearest to the exit sideof the cemented lens has a value size enough to make changes in thetilts of lens surfaces small upon adjustment of relative lens centers sothat the relative lens centers can be corrected by shifting of the lenssurfaces. It is thus possible to simultaneously keep center and off-axisperformances against deteriorations from design values.

Condition (14) defines the shape of the lens nearest to the image planeside of the cemented lens, and shows that by making the radius ofcurvature of the cementing surface R₂ large, the tilts of the lensesoccurring upon adjustment of the relative lens centers are reduced toprevent performance deteriorations.

According to the fourth embodiment of the second aspect of theinvention, there is provided an optical system, characterized bycomprising a cemented lens having a cementing surface on an optical axisof the optical system, wherein lenses that form said cemented lenssatisfy conditions (15) and (16):40<ν_(max)−ν_(min)<80   (15)23.7>ν_(min)   (16)where ν_(max) is the maximum of Abbe constants that the lenses in saidcemented lens have, and

ν_(min) is the minimum of Abbe constants that the lenses in saidcemented lens have.

The advantage of, and the requirement for, the fourth optical system setup as recited above is now explained.

Optical systems comprising a cemented lens with chromatic aberrationscorrected with the type of vitreous material of the lenses used havealready been proposed in the art. With any of those optical systems,however, it is still difficult to gain high optical performances overthe entire zoom range, because the Abbe constant of the lenses formingthe cemented lens is larger than represented by condition (16), and thevitreous material used deviates from the range of condition (15).

In the invention, the materials, etc. of the respective lenses that formthe cemented lens are properly determined, thereby providing an opticalsystem capable of satisfactory correction of chromatic aberrations inparticular over the entire zoom range.

A deviation from the lower limit to the range of condition (15), thatis, 40, will result in under-correction of chromatic aberrations, and adeparture from the upper limit to the range of condition (15), that is,80, will lead to overcorrection.

According to the fifth embodiment of the second aspect of the invention,there is provided an optical system, characterized by comprising acemented lens having a cementing surface on an optical axis of theoptical system, wherein lenses that form said cemented lens satisfyconditions (15), (16), (17), (18) and (19):40<ν_(max)−ν_(min)<80   (15)23.7>ν_(min)   (16)60<νmax   (17)1.8<n_(dmax)   (18)1.55>n_(dmin)   (19)where ν_(max) is the maximum of Abbe constants that the lenses in saidcemented lens have,

ν_(min) is the minimum of Abbe constants that the lenses in saidcemented lens have,

n_(dmax) is the maximum of refractive indices that the lenses in saidcemented lens have, and

n_(dmin) is the minimum of refractive indices that the lenses in saidcemented lens have.

The advantage of, and the requirement for, the fifth optical system setup as recited above is now explained.

Optical systems comprising a cemented lens with chromatic aberrationscorrected with the type of vitreous material of the lenses used havealready been proposed in the art. With any of those optical systems,however, it is still difficult to gain high optical performances overthe entire zoom range, because vitreous materials having refractiveindices and Abbe constants deviating from the ranges defined byconditions (15) to (19) are used for the lenses forming the cementedlens, resulting in,difficulty in correction of chromatic aberrations inparticular.

In the invention, the materials, etc. of the lenses that form thecemented lens are properly determined, thereby providing an opticalsystem capable of satisfactory correction of chromatic aberrations inparticular over the entire zoom range.

A deviation from the lower limit to the range of condition (15), thatis, 40, will result in under-correction of chromatic aberrations, and adeparture from the upper limit to the range of condition (15), that is,80, will lead to overcorrection.

When there is any departure from the range of condition (18) or theminimum of the refractive indices that the lenses forming the cementedlens have is less than 1.8, field curvature and spherical aberrationswill occur.

According to the sixth embodiment of the second aspect of the invention,either one of the 4^(th) and 5^(th) optical systems is furthercharacterized by comprising two lens groups, i.e., a lens group ofnegative refracting power and a lens group of positive refracting power.

The advantage of, and the requirement for, the 6^(th) optical system setup as recited above is now explained.

Such a two-group arrangement comprising a lens group of negativerefracting power and a lens group of positive refracting power is theleast requirement for gaining a zoom ratio of as high as 2 or greaterwith well-corrected aberrations. A combination of that requirement withthe condition for the third optical system of the second aspect of theinvention ensures further size reductions, because the powers of otherlenses can be enhanced.

According to the seventh embodiment of the second aspect of theinvention, any one of the 1^(st) to 6^(th) optical systems is furthercharacterized in that at least one of air contact surfaces on the lightray entrance and exit sides of said cemented lens is aspheric.

The advantage of, and the requirement for, the seventh optical systemset up as recited above is now explained.

Although the cementing of three or more lenses including at least onenegative lens causes aberration correction capability to become low inproportion to fewer lens elements, yet this can be compensated for byusing an aspheric surface for at least one of the air contact surfacesof the cemented lens with the result that the whole optical system canbe further slimmed down. Especially if this requirement is combined withcondition (11) or (13), severer fabrication tolerances imposed by thelocation of the aspheric surface are then lessened by enhanced centeradjustment effects, thereby ensuring ease of fabrication.

According to the eighth embodiment of the second aspect of theinvention, any one of the 1^(st) to 7^(th) optical systems is furthercharacterized in that said cemented lens consists of three lenses.

The advantage of, and the requirement for, the eighth optical system setup as recited above is now explained.

Use of the cemented lens with three lenses cemented together enableschromatic aberrations to be full-corrected, and the cementing of threelenses helps hold back performance degradation by decentration, becausethe amount of decentration of lens elements can be easily reduced.

According to the ninth embodiment of the second aspect of the invention,any one of the 1^(st) to 8^(th) optical systems is further characterizedin that said second lens group comprises a triplet lens wherein apositive first lens, a negative second lens and a positive third lensare arranged in order from its object side.

The advantage of, and the requirement for, the ninth optical system setup as recited above is now explained.

By incorporating in the second lens group an optical system in which thepositive first lens, the negative second lens and the positive thirdlens are arranged in order from its object side, axial aberrations,field curvature and chromatic aberrations are primarily wellcorrectable.

According to the 10^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 9^(th) optical systems is furthercharacterized in that the second lens group consists only of the tripletlens.

The advantage of, and the requirement for, the 10^(th) optical systemset up as recited above is now explained.

With the second lens group consisting only of the triplet lens,compactness is achievable while aberrations inclusive of chromaticaberrations are well balanced.

According to the 11^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 10^(th) optical systems is furthercharacterized in that focusing is carried out by movement of one groupof lenses.

The advantage of, and the requirement for, the 11^(th) optical systemset up as recited above is now explained.

Such an arrangement is simple in mechanism, and helps reduce aberrationfluctuations from the wide-angle end to the telephoto end.

According to the 12^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 11^(th) optical systems is furthercharacterized in that said second lens group moves monotonously from theimage plane side to the object side, and said first lens group moves ina convex locus toward the image plane side.

The advantage of, and the requirement of, the 12^(th) optical system setup as recited above is now explained.

Such an arrangement is simple in mechanism, and enables the total lengthof the lens system to be shortened upon taking. When the aperture stopis located in unison with the second lens group, it is possible to makethe diameter of the first lens group small because the entrance pupil inthe wide-angle mode is set at a shallow position.

According to the 13^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 3^(rd) optical systems is furthercharacterized by satisfying condition (15):40<ν_(max)−ν_(min)<80   (15)where ν_(max) is the maximum of Abbe constants that the lenses in saidcemented lens have, and

ν_(min) is the minimum of Abbe constants that the lenses in saidcemented lens have.

The advantage of, and the requirement for, the 13^(th) optical systemset up as recited above is now explained.

When the Abbe constant difference between the lenses forming thecemented lens satisfies condition (15), the optical system is wellcorrected primarily for chromatic aberrations, guaranteeing compactnessand high optical performance all over the zoom range. Especially when itcomes to a lens system made up of a cemented lens and other lens orlenses, the ability of the cemented lens to correct chromaticaberrations is so enhanced that the power of other lens system can beincreased with fewer lenses, achieving compactness and making it easyfor a zoom lens to have a high zoom ratio.

According to the 14^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 12^(th) optical systems is furthercharacterized in that the lens nearest to the object side of the tripletlens and the lens nearest to the image plane side thereof are formed ofthe same vitreous material.

The advantage of, and the requirement for, the 14^(th) optical systemset up as recited above is now explained.

Use of the same vitreous material helps reduce the types of the vitreousmaterials used, making fabrication management easy and achieving costreductions.

According to the 15^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 3^(rd) and the 6^(th) to 14^(th)optical systems is further characterized in that said cemented lens isconcave on its object side, and further satisfies condition (20):0.50<D _(n1) /Σd<0.95   (20)where D_(n1) is a distance from the surface located in said cementedlens and nearest to its object side to the surface having the largestnegative refracting power in said cemented lens, and

Σd is the total thickness of said cemented lens.

The advantage of, and the requirement for, the 15^(th) optical systemset up as recited above is now explained.

Satisfaction of condition (20) permits the surface of negative power inthe cemented lens to be suitably spaced away from the object-sidesurface having positive power, so that with chromatic aberrationscorrected, the principal points of the second lens group especially atthe telephoto end come close to the first lens group. This works forachievement of high zoom ratios.

As the upper limit of 0.95 to condition (2) is exceeded, it renders itdifficult to fabricate the subsequent lens (located on the image planeside with respect to the negative power surface in the cemented lens),because its thickness becomes too small. As the lower limit of 0.50 isnot reached, it causes the surface of negative power to come too closeto the entrance surface (nearest to the object side), rendering controlof the principal points difficult and high zoom ratios hard to achieve.

According to the 16^(th) embodiment of the second aspect of theinvention, the 15^(th) optical system is further characterized bysatisfying condition (21):0.05<D _(n2) /Σd<0.35   (21)where D_(n2) is a distance from the surface having the largestrefracting power in said cemented lens to the surface located in saidcemented lens and nearest to its image plane side.

The advantage of, and the requirement for, the 16^(th) optical systemset up as recited above is now explained.

Satisfaction of condition (21) makes the distance from the surface ofnegative power in the cemented lens to the exit surface (nearest to theimage plane side) so moderately short that the positions of theprincipal points of the second lens group can be suitably controlled toachieve a high zoom ratio and gain compactness upon the optical systemreceived at a collapsible lens mount.

As the upper limit of 0.35 to condition (21) is exceeded, it worksagainst compactness upon the optical system received at a collapsiblelens mount, because the cemented lens becomes too thick. Otherwise,difficulty is encountered in bringing the principal point positions atthe telephoto end in particular close to the first lens group, workingagainst achieving high zoom ratios. As the lower limit of 0.05 is notreached, a fabrication problem arises because the thickness of lensesfrom the negative power surface to the exit surface becomes too small.

According to the 17^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 3^(rd) and the 6^(th) to 16^(th)optical systems is further characterized in that said cemented lens isconvex on its object side, and further satisfies condition (22):−1.5<(r ₁ +r ₂)/(r ₁ −r ₂)<−0.5   (22)where r₁ is the radius of curvature of the surface nearest to the objectside of said cemented lens, and

r₂ is the radius of curvature of the surface nearest to the image planeside of said cemented lens.

The advantage of, and the requirement for, the 17^(th) optical systemset up as recited above is now explained.

Condition (22) defines the shape of the cemented lens. Morespecifically, the cemented lens is configured such that its mainpositive power is allocated to the entrance surface (nearest to theobject side). This is an arrangement favorable for achieving sizereductions and high zoom ratios while various aberrations are correctedin a well-balanced state.

As the upper limit of −0.5 to condition (22) is exceeded, the power ofthe entrance surface becomes weak (or the power of the exit surfacebecomes strong), rendering control of the principal point positions atthe telephoto end in particular difficult. Otherwise, it is difficult toslim down the lens located in the cemented lens and nearer to its imageplane side, rendering size reductions difficult. As the lower limit of−1.5 is not reached, the power of the entrance surface becomes toostrong (or the power of the exit surface tends to become negative),rendering relative correction of aberrations difficult.

According to the 18^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 3^(rd) and the 6^(th) to 17^(th)optical systems is further characterized in that said cemented lens isconvex on its object side, and said negative lens is cemented to theimage plane side of the lens nearest to the object side, withsatisfaction of conditions (23) and (24):−1.0<R ₁ /F ₂<−0.05   (23)0.50<D ₁ /Σd<0.95   (24)where R₁ is the radius of curvature of the cementing surface located insaid cemented lens and nearest to its object side,

F₂ is the focal length of said second lens group,

D₁ is the axial thickness of the lens located in said cemented lens andnearest to its object side, and

Σd is the total thickness of said cemented lens.

The advantage of, and the requirement for, the 18^(th) optical systemset up as recited above is now explained.

As the negative lens is cemented to the lens in the cemented lens, whichis located nearest to its object side, and the cementing surface in thecemented lens, which is nearest to its object side, is allowed to havenegative power large enough to satisfy condition (23), it makes goodcorrection of chromatic aberrations (especially longitudinal chromaticaberration) while achieving compactness. Further, as this surface ofnegative power is spaced away from the entrance surface in such a way asto satisfy condition (24), it enables the principal point positions ofthe second lens group especially at the telephoto end to come so closeto the first lens group that high zoom ratios are achievable withvarious aberrations corrected in a well-balanced state.

As the upper limit of −0.05 to condition (23) is exceeded, the curvature(power) of the cementing surface on the object side becomes too tight,and upon adjustment of relative lens centers, there is a large change inthe tilts of the lenses. This in turn causes center or off-axisperformances to be apart from the design values, even when the relativelens centers are corrected by shifting of the lens surfaces. As thelower limit of −1.0 is not reached, the curvature (power) of thecementing surface nearest to the object side becomes too loose,rendering chromatic aberrations hard to correct.

As the upper limit of 0.95 to condition (24) is exceeded, it renders itdifficult to fabricate the subsequent lens (located on the image planeside with respect to the lens nearest to the object side of the cementedlens), because its thickness becomes too small. Otherwise, the cementedlens becomes too thick for compactness. As the lower limit of 0.50 isnot reached, it causes the surface of negative power to come too closeto the entrance surface (nearest to the object side), rendering controlof the principal points difficult and high zoom ratios hard to achieve.

According to the 19^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 3^(rd) and the 6^(th) to 17^(th)optical systems is further characterized in that said cemented lens isconvex on its object side, and said negative lens is cemented to thelens located in said cemented lens and nearest to its image plane side,with satisfaction of conditions (25) and (26):2.5<|R ₁ /F ₂|  (25)0.45<R ₂ /F ₂<2.3   (26)where R₁ is the radius of curvature of the cementing surface located insaid cemented lens and nearest to its object side,

F₂ is the focal length of the second lens group, and

R₂ is the radius of curvature of the cementing surface located in saidcemented lens and nearest to its image plane side.

The advantage of, and the requirement for, the 19^(th) optical systemset up as recited above is now explained.

As satisfaction of condition (25) allows the cementing surface nearestto the object side of the cemented lens to have weak positive ornegative power, it works for mitigating the influences of decentration.It also enables the cementing surface nearest to the object side to comeso close to a planar surface while keeping the power of the cementedlens intact, so that the radius of curvature of each lens located on theimage plane side with respect to the lens nearest to the object sidebecomes large (or each lens comes close to a planar surface). This inturn enables the subsequent lenses (on the image plane side with respectto the cementing surface nearest to the object side) to be made so thinthat compactness, slimming and cemented lens fabrication are easilyachievable. As satisfaction of condition (26) allows the cementingsurface located in the cemented lens and nearest to its image plane sideto have negative power, it is good for correction of chromaticaberrations. It also works for high zoom ratios, because the principalpoint positions of the second lens group at a cementing surface awayfrom the entrance surface (nearest to the object side) and especially atthe telephoto end come close to the first lens group.

As the lower limit of 2.5 to condition (25) is not reached, thecurvature of the cementing surface nearest to the object side becomestoo tight, and upon adjustment of relative lens centers, there is anincreasing change in the tilts of the lens surfaces. As a result, thereare center or off-axis performance deteriorations from the designvalues, even when the relative centers are corrected by shifting of thelens surfaces.

As the upper limit of 2.3 to condition (26) is exceeded, the curvatureof the cementing surface nearest to the image plane side slacks,rendering chromatic aberrations hard to correct. Otherwise, there is aneed for the other lens (such as the cementing surface nearest to theobject side) to have an increased power for correction of chromaticaberrations. To, in this case, bring the principal point positions ofthe second lens group at the telephoto end close to the first lens groupfor the purpose of high zoom ratios, a thicker lens must be used tospace the entrance surface suitably away from the lens surface havingthat negative power, often failing to achieve compactness. As the lowerlimit of 0.45 is not reached, the curvature of the cementing surfacenearest to the image plane side becomes too tight. This requires for thesurface nearest to the object side to have a tighter curvature tocorrect various aberrations in a well-balanced state with the resultthat the lens nearest to the image plane side tends to become thick.Otherwise, the surface nearest to the image plane side tends to havenegative power, and there is a need for the surface nearest to theobject side to have a tighter curvature to keep the power of thecemented lens, resulting in difficulty in relative correction of variousaberrations.

According to the 20^(th) embodiment of the second aspect of theinvention, the 19^(th) optical system is further characterized bysatisfaction of conditions (22) and (27):−1.5<(r ₁ +r ₂)/(r ₁ −r ₂)<−0.5   (22)0.05<D ₃ /Σd<0.30   (27)where r₁ is the radius of curvature of the surface nearest to the objectside of said cemented lens,

r₂ is the radius of curvature of the surface nearest to the image planeside of said cemented lens,

D₃ is the axial thickness of the lens located in said cemented lens andnearest to its image plane side, and

Σd is the total thickness of said cemented lens.

The advantage of, and the requirement for, the 20^(th) optical systemset up as recited above is now explained.

Satisfaction of condition (22) allows the main positive power of thecemented lens to be allocated to the entrance surface (nearest to theobject side). This works for compactness and high zoom ratios whilevarious aberrations are corrected in a well-balanced state. Simultaneoussatisfaction of conditions (22) and (26) enables the lens located in thecemented lens and nearest to its image side to be made thin enough tosatisfy condition (27). This is favorable for high zoom ratios, becausethe surface subsequent to the cementing surface of negative powernearest to the image plane side comes close to that cementing surfacenearest to the image plane side, and so the principal point positions ofthe second lens group especially at the telephoto end comes close to thefirst lens group.

As the upper limit of −0.5 to condition (22) is exceeded, the power ofthe entrance surface becomes weak (or the power of the exit surfacebecomes strong), rendering adjustment of the principal point positionsespecially at the telephoto end difficult. Otherwise, it is difficult tothin the lens located in the cemented lens and nearer to its imageplane, and so achieve compactness. Falling short of the lower limit of−1.5 causes the power of the entrance surface to become too strong (orit causes the power of the exit surface to be likely to be negative),rendering relative correction of aberrations difficult.

Exceeding the upper limit of 0.30 to condition (27) causes the cementedlens to tend to become thick, resulting difficulty in achievingcompactness. Otherwise, the curvature of the surface nearest to theimage plane side becomes too tight to adjust the principal pointpositions. Falling short of the lower limit of 0.05 causes the surfacenearest to the image plane side to come too close to the cementingsurface nearest to the image plane side. In other words, the lensnearest to the image plane side becomes too thin to fabricate.

According to the 21^(st) embodiment of the second aspect of theinvention, any one of the 1^(st) to 3^(rd) and the 6^(th) to 20^(th)optical systems is further characterized by satisfaction of conditions(25) and (16):40<ν_(max)−ν_(min)<80   (25)23.7>ν_(min)   (16)where ν_(max) is the maximum of Abbe constants that the lenses in saidcemented lens have, and

ν_(min) is the minimum of Abbe constants that the lenses in saidcemented lens have.

The advantage of, and the requirement for, the 21^(st) optical systemset up as recited above is now explained.

Optical systems comprising a cemented lens with chromatic aberrationscorrected with the type of vitreous material of the lenses used havealready been proposed in the art. With any of those optical systems,however, it is still difficult to gain high optical performances overthe entire zoom range, because the Abbe constant of the lenses formingthe cemented lens is larger than represented by condition (16), and thevitreous material used deviates from the range of condition (25).

In the invention, the materials, etc. of the respective lenses that formthe cemented lens are properly determined, thereby providing an opticalsystem capable of satisfactory correction of chromatic aberrations inparticular over the entire zoom range.

A deviation from the lower limit to the range of condition (25), thatis, 40, will result in under-correction of chromatic aberrations, and adeparture from the upper limit to the range of condition (25), that is,80, will lead to overcorrection.

According to the 22^(nd) embodiment of the second aspect of theinvention, the 21^(st) optical system is further characterized bysatisfying conditions (17), (18) and (19):60<νmax   (17)1.8<n_(dmax)   (18)1.55>n_(dmin)   (19)where ν_(max) is the maximum of Abbe constants that the lenses in saidcemented lens have,

n_(dmax) is the maximum of refractive indices that the lenses in saidcemented lens have, and

n_(dmin) is the minimum of refractive indices that the lenses in saidcemented lens have.

The advantage of, and the requirement for, the 22^(nd) optical systemset up as recited above is now explained.

Optical systems comprising a cemented lens with chromatic aberrationscorrected with the type of vitreous material of the lenses used havealready been proposed in the art. With any of those optical systems,however, it is still difficult to gain high optical performances overthe entire zoom range, because vitreous materials having refractingindices and Abbe constants deviating from the ranges defined byconditions (17) to (19) are used for the lenses forming the cementedlens, resulting in difficulty in correction of chromatic aberrations inparticular.

In the invention, the materials, etc. of the lenses that form thecemented lens are properly determined, thereby providing an opticalsystem capable of satisfactory correction of chromatic aberrations inparticular over the entire zoom range.

When there is a departure from the range of condition (18) or themaximum of the refractive indices that the lenses in the cemented lenshave does not reach 1.8, field curvature and spherical aberrations willoccur.

According to the 23^(rd) embodiment of the second aspect of theinvention, either one of the 4^(th) and 5^(th) optical systems isfurther characterized in that said cemented lens includes at least onepositive lens and at least one negative lens.

The advantage of, and the requirement for, the 23^(rd) optical systemset up as recited above is now explained.

Incorporation of at least one positive lens and at least one negativelens in the cemented lens makes good correction of chromatic aberrationspossible. In this case, the Abbe constant of the negative lens ispreferably smaller than that of the positive lens.

According to the 24^(th) embodiment of the second aspect of theinvention, any one of the 1^(st) to 23^(rd) optical systems is furthercharacterized in that said cemented lens has a double-convex form at ornear the optical axis.

The advantage of, and the requirement for, the 24^(th) optical systemset up as recited above is now explained.

With the double-convex form of the cemented lens, it is possible tobring the entrance and exit surfaces of the cemented lens approximate toa symmetric system that ensures that various aberrations are more easilycorrected in a well-balanced state.

According to the 25^(th) embodiment of the second aspect of theinvention, any one of the 7^(th) to 24^(th) optical systems is furthercharacterized in that said exit-side aspheric surface is configured insuch a way as to have an increasing divergent effect with distance ofthe center of the lens.

The advantage of, and the requirement for, the 25^(th) optical systemset up as recited above is now explained.

Provision of such an aspheric surface ensures that axial and off-axisaberrations are correctable at the surface nearest to the image planeside in a well-balanced state.

The present invention also encompasses an imaging system, characterizedby comprising any one of the 1^(st) to 25^(th) optical systems accordingto the second aspect of the invention, and further comprising anelectronic image pickup device for converting an optical image formedthrough said optical system into electric signals.

The imaging system has the same advantages and requirements as alreadydescribed.

More preferable ranges of conditions (11) to (27) as mentioned above areset out below. In the values given below, the rightmost one is the mostpreferable limit. Condition Lower Value Upper Value (11) —0.93/0.85/0.80 (12) 1.0/2.0/2.5 15/10/7.5/5.5 (13) 12/14.5/20 — (14)0.75/0.80 — (15) — 70/60/55 (16) — 23.0/22.5 (17) 63.5/64.0 — (18) — —(19) — — (20) 0.60/0.68 0.90/0.85 (21) 0.08/0.10/0.12 0.32/0.30/0.25(22) −1.3/−1.0 −0.65/−0.70/−0.80/−0.85 (23) −0.90 −0.25/−0.35/−0.50 (24)0.55/0.60 0.85/0.80/0.75 (25) 3.0/4.5/5.0 —/5.5/6.5/9.0 (26) 0.5/0.6/0.72.0/1.5 (27) 0.08/0.11 0.25/0.22

It is herein understood that some or all of the above conditions shouldpreferably be satisfied at the same time.

With the invention as detailed above, it is possible to obtain a zoomlens of improved image-formation capability with a reduced number oflenses, and fabricate a slim yet high-performance digital or videocamera.

It is also possible to obtain an optical system which, albeit havinghigh zoom ratios, can be slimmed down with performance deteriorationsminimized by reduced influences of decentration, and so achieve a slimyet high-performance digital or video camera having high zoom ratios.

The present invention is now explained in further details with referenceto Examples 1 to 17. FIGS. 1(a), 1(b) and 1(c) through FIGS. 17(a),17(b) and 17(c) are illustrative in lens section of Examples 1 to 17 attheir wide-angle end, in their intermediate setting and at theirtelephoto end, respectively, upon focusing on an infinite object point.In these drawings, a first lens group is indicated at G1, an aperturestop at S, a second lens group at G2, a third lens group at G3, aplane-parallel plate such as a filter at P, a plane-parallel plate thatforms a low-pass filter provided with a wavelength limiting coating forlimiting infrared light, etc. at F, a cover glass for an image pickupdevice at C, and an image plane at I.

EXAMPLE 1

As shown in FIG. 1, Example 1 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S and a second lens group G2 havingpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina concave locus toward the object side, and is positioned nearer to theimage plane side of the zoom lens system at the telephoto end than atthe wide-angle end. The second lens group G2 moves monotonously towardthe object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, adouble-convex positive lens, a double-concave negative lens and adouble-convex positive lens. Three aspheric surfaces are used: one forthe image plane-side surface of the negative meniscus lens in the firstlens group G1, one for the surface nearest to the object side of thetriplet lens forming the second lens group G2, and one for the surfacenearest to the image plane side thereof.

EXAMPLE 2

As shown in FIG. 2, Example 2 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S and a second lens group G2 havingpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina concave locus toward the object side, and is positioned nearer to theimage plane side of the zoom lens system at the telephoto end than atthe wide-angle end. The second lens group G2 moves monotonously towardthe object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, apositive meniscus lens convex on its object side, a negative meniscuslens convex on its object side and a double-convex positive lens. Threeaspheric surfaces are used: one for the image plane-side surface of thenegative meniscus lens in the first lens group G1, one for the surfacenearest to the object side of the triplet lens forming the second lensgroup G2, and one for the surface nearest to the image plane-sidethereof.

EXAMPLE 3

As shown in FIG. 3, Example 3 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S and a second lens group G2 havingpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina concave locus toward the object side, and is positioned nearer to theimage plane side of the zoom lens system at the telephoto end than atthe wide-angle end. The second lens group G2 moves monotonously towardthe object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, apositive meniscus lens convex on its object side, a negative meniscuslens convex on its object side and a double-convex positive lens. Threeaspheric surfaces are used: one for the image plane-side surface of thenegative meniscus lens in the first lens group G1, one for the surfacenearest to the object side of the triplet lens forming the second lensgroup G2, and one for the surface nearest to the image plane-sidethereof.

EXMAPLE 4

As shown in FIG. 4, Example 4 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S and a second lens group G2 havingpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina concave locus toward the object side, and is positioned nearer to theimage plane side of the zoom lens system at the telephoto end than atthe wide-angle end. The second lens group G2 moves monotonously towardthe object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, apositive meniscus lens convex on its object side, a negative meniscuslens convex on its object side and a double-convex positive lens. Threeaspheric surfaces are used: one for the image plane-side surface of thenegative meniscus lens in the first lens group G1, one for the surfacenearest to the object side of the triplet lens forming the second lensgroup G2, and one for the surface nearest to the image plane-sidethereof.

EXMAPLE 5

As shown in FIG. 5, Example 5 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S and a second lens group G2 havingpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina concave locus toward the object side, and is positioned nearer to theimage plane side of the zoom lens system at the telephoto end than atthe wide-angle end. The second lens group G2 moves monotonously towardthe object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, adouble-convex positive lens, a double-concave negative lens and adouble-convex positive lens. Three aspheric surfaces are used: one forthe image plane-side surface of the negative meniscus lens in the firstlens group G1, one for the surface nearest to the object side of thetriplet lens forming the second lens group G2, and one for the surfacenearest to the image plane-side thereof.

EXMAPLE 6

As shown in FIG. 6, Example 6 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S, a second lens group G2 havingpositive refracting power and a third lens group G3 having positiverefracting power. Upon zooming from the wide-angle end to the telephotoend of the zoom lens system, the first lens group G1 moves in a concavelocus toward the object side, and is positioned nearer to the objectside of the zoom lens system at the telephoto end than at the wide-angleend. The second lens group G2 moves monotonously toward the object sidein unison with the aperture stop S. The third lens group G3 moves in aconcave locus toward the object side, and is positioned nearer to theobject side at the telephoto end than at the wide-angle end.

The first lens group G1 is composed of, in order from its object side, adouble-concave negative lens and a positive meniscus lens convex on itsobject side, the second lens group G2 is composed of a triplet lensconsisting of, in order from its object side, a positive meniscus lensconvex on its object side, a negative meniscus lens convex on its objectside and a double-convex positive lens, and the third lens group G3 iscomposed of one double-convex positive lens. Three aspheric surfaces areused: one for the image plane-side surface of the double-concavenegative lens in the first lens group G1, one for the surface nearest tothe object side of the triplet lens forming the second lens group G2,and one for the surface nearest to the image plane-side thereof.

EXAMPLE 6

As shown in FIG. 6, Example 6 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S, a second lens group G2 havingpositive refracting power and a third lens group G3 having positiverefracting power. Upon zooming from the wide-angle end to the telephotoend of the zoom lens system, the first lens group G1 moves in a concavelocus toward the object side, and is positioned nearer to the objectside of the zoom lens system at the telephoto end than at the wide-angleend. The second lens group G2 moves monotonously toward the object sidein unison with the aperture stop S. The third lens group G3 moves in aconcave locus toward the object side, and is positioned nearer to theobject side at the telephoto end than at the wide-angle end.

The first lens group G1 is composed of, in order from its object side, adouble-concave negative lens and a positive meniscus lens convex on itsobject side, the second lens group G2 is composed of a triplet lensconsisting of, in order from its object side, a positive meniscus lensconvex on its object side, a negative meniscus lens convex on its objectside and a double-convex positive lens, and the third lens group G3 iscomposed of one double-convex positive lens. Three aspheric surfaces areused: one for the image plane-side surface of the double-concavenegative lens in the first lens group G1, one for the surface nearest tothe object side of the triplet lens forming the second lens group G2,and one for the surface nearest to the image plane-side thereof.

EXMAPLE 7

As shown in FIG. 7, Example 7 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S, a second lens group G2 havingpositive refracting power and a third lens group G3 having positiverefracting power. Upon zooming from the wide-angle end to the telephotoend of the zoom lens system, the first lens group G1 moves toward theobject side. The second lens group G2 moves monotonously toward theobject side in unison with the aperture stop S. The third lens group G3moves in a concave locus toward the object side, and is positionednearer to the object side at the telephoto end than at the wide-angleend.

The first lens group G1 is composed of, in order from its object side, adouble-concave negative lens and a positive meniscus lens convex on itsobject side, the second lens group G2 is composed of a triplet lensconsisting of, in order from its object side, a positive meniscus lensconvex on its object side, a negative meniscus lens convex on its objectside and a double-convex positive lens, and the third lens group G3 iscomposed of one double-convex positive lens. Three aspheric surfaces areused: one for the image plane-side surface of the double-concavenegative lens in the first lens group G1, one for the surface nearest tothe object side of the triplet lens forming the second lens group G2,and one for the surface nearest to the image plane-side thereof.

EXMAPLE 8

As shown in FIG. 8, Example 8 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S and a second lens group G2 havingpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina convex locus toward the image plane side of the zoom optical system,and is positioned nearer to the image plane side at the telephoto endthan at the wide-angle end. The second lens group G2 moves monotonouslytoward the object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, apositive meniscus lens convex on its object side, a negative meniscuslens convex on its object side and a double-convex positive lens. Threeaspheric surfaces are used: one for the image plane-side surface of thenegative meniscus lens in the first lens group G1, one for the surfacenearest to the object side of the triplet lens forming the second lensgroup G2, and one for the surface nearest to the image plane-sidethereof.

EXAMPLE 9

As shown in FIG. 9, Example 9 is directed to a zoom optical system madeup of, in order its object side, a first lens group G1 having negativerefracting power, an aperture stop S and a second lens group G2 havingpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina convex locus toward the image plane side of the zoom optical system,and is positioned nearer to the image plane side at the telephoto endthan at the wide-angle end. The second lens group G2 moves monotonouslytoward the object side in unison with the aperture stop S.

The first-lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, apositive meniscus lens convex on its object side, a negative meniscuslens convex on its object side and a double-convex positive lens. Threeaspheric surfaces are used: one for the image plane-side surface of thenegative meniscus lens in the first lens group G1, one for the surfacenearest to the object side of the triplet lens forming the second lensgroup G2, and one for the surface nearest to the image plane-sidethereof.

EXAMPLE 10

As shown in FIG. 10, Example 10 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S and a second lens group G2having positive refracting power. Upon zooming from the wide-angle endto the telephoto end of the zoom lens system, the first lens group G1moves in a convex locus toward the image plane side of the zoom opticalsystem, and is positioned nearer to the image plane side at thetelephoto end than at the wide-angle end. The second lens group G2 movesmonotonously toward the object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, aplano-convex lens convex on its object side, a plano-concave negativelens and a double-convex positive lens. Three aspheric surfaces areused: one for the image plane-side surface of the negative meniscus lensin the first lens group G1, one for the surface nearest to the objectside of the triplet lens forming the second lens group G2, and one forthe surface nearest to the image plane-side thereof.

EXAMPLE 11

As shown in FIG. 11, Example 11 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S and a second lens group G2having positive refracting power. Upon zooming from the wide-angle endto the telephoto end of the zoom lens system, the first lens group G1moves in a convex locus toward the image plane side of the zoom opticalsystem, and is positioned nearer to the image plane side at thetelephoto end than at the wide-angle end. The second lens group G2 movesmonotonously toward the object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet consisting of, in order from its object side, adouble-convex positive lens, a double-concave negative lens and adouble-convex positive lens. Three aspheric surfaces are used: one forthe image plane-side surface of the negative meniscus lens in the firstlens group G1, one for the surface nearest to the object side of thetriplet lens forming the second lens group G2, and one for the surfacenearest to the image plane-side thereof.

EXAMPLE 12

As shown in FIG. 12, Example 12 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S and a second lens group G2having positive refracting power. Upon zooming from the wide-angle endto the telephoto end of the zoom lens system, the first lens group G1moves in a convex locus toward the image plane side of the zoom opticalsystem, and is positioned nearer to the image plane side at thetelephoto end than at the wide-angle end. The second lens group G2 movesmonotonously toward the object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet consisting of, in order from its object side, adouble-convex positive lens, a negative meniscus lens convex on itsimage plane side and a negative meniscus lens convex on its image planeside. Three aspheric surfaces are used: one for the image plane-sidesurface of the negative meniscus lens in the first lens group G1, onefor the surface nearest to the object side of the triplet lens formingthe second lens group G2, and one for the surface nearest to the imageplane-side thereof.

EXMAPLE 13

As shown in FIG. 13, Example 13 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S and a second lens group G2having positive refracting power. Upon zooming from the wide-angle endto the telephoto end of the zoom lens system, the first lens group G1moves in a convex locus toward the image plane side of the zoom opticalsystem, and is positioned nearer to the object side at the telephoto endthan at the wide-angle end. The second lens group G2 moves monotonouslytoward the object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, apositive meniscus lens convex on its object side, a negative meniscuslens convex on its object side and a double-convex positive lens. Threeaspheric surfaces are used: one for the image plane-side surface of thenegative meniscus lens in the first lens group G1, one for the surfacenearest to the object side of the triplet lens forming the second lensgroup G2, and one for the surface nearest to the image plane-sidethereof.

EXMAPLE 14

As shown in FIG. 14, Example 14 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S and a second lens group G2having positive refracting power. Upon zooming from the wide-angle endto the telephoto end of the zoom lens system, the first lens group G1moves in a convex locus toward the image plane side of the zoom opticalsystem, and is positioned nearer to the image plane side at thetelephoto end than at the wide-angle end. The second lens group G2 movesmonotonously toward the object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, adouble-convex positive lens, a negative meniscus lens convex on itsimage plane side and a positive meniscus lens convex on its image planeside. Three aspheric surfaces are used: one for the image plane-sidesurface of the negative meniscus lens in the first lens group G1, onefor the surface nearest to the object side of the triplet lens formingthe second lens group G2, and one for the surface nearest to the imageplane-side thereof.

EXMAPLE 15

As shown in FIG. 15, Example 15 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S and a second lens group G2having positive refracting power. Upon zooming from the wide-angle endto the telephoto end of the zoom lens system, the first lens group G1moves in a convex locus toward the image plane side of the zoom opticalsystem, and is positioned nearer to the image plane side at thetelephoto end than at the wide-angle end. The second lens group G2 movesmonotonously toward the object side in unison with the aperture stop S.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, and the second lens group G2 is composedof a triplet lens consisting of, in order from its object side, apositive meniscus lens convex on its object side, a positive meniscuslens convex on its object side and a double-convex positive lens. Threeaspheric surfaces are used: one for the image plane-side surface of thenegative meniscus lens in the first lens group G1, one for the surfacenearest to the object side of the triplet lens forming the second lensgroup G2, and one for the surface nearest to the image plane-sidethereof.

EXAMPLE 16

As shown in FIG. 16, Example 16 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S, a second lens group G2having positive refracting power and a third lens group G3 having weaknegative refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina convex locus toward the image plane side of the zoom optical system,and is positioned nearer to the image plane side at the telephoto endthan at the wide-angle end. The second lens group G2 moves monotonouslytoward the object side in unison with the aperture stop S, and the thirdlens group G3 moves toward the image plane side for compensation for animage plane.

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, the second lens group G2 is composed ofa triplet consisting of, in order from its object side, a positivemeniscus lens convex on its object side, a negative meniscus lens convexon its object side and a double-convex positive lens, and the third lensgroup G3 is composed of one negative meniscus lens convex on its objectside. Three aspheric surfaces are used: one for the image plane-sidesurface of the negative meniscus lens in the first lens group G1, onefor the surface nearest to the object side of the triplet lens formingthe second lens group G2, and one for the surface nearest to the imageplane-side thereof.

EXAMPLE 17

As shown in FIG. 17, Example 17 is directed to a zoom optical systemmade up of, in order its object side, a first lens group G1 havingnegative refracting power, an aperture stop S, a second lens group G2having positive refracting power and a third lens group G3 having weakpositive refracting power. Upon zooming from the wide-angle end to thetelephoto end of the zoom lens system, the first lens group G1 moves ina convex locus toward the image plane side of the zoom optical system,and is positioned nearer to the image plane side at the telephoto endthan at the wide-angle end. The second lens group G2 moves monotonouslytoward the object side in unison with the aperture stop S, and the thirdlens group G3 remains fixed

The first lens group G1 is composed of, in order from its object side, anegative meniscus lens convex on its object side and a positive meniscuslens convex on its object side, the second lens group G2 is composed ofa triplet consisting of, in order from its object side, a positivemeniscus lens convex on its object side, a, negative meniscus lensconvex on its object side and a double-convex positive lens, and thethird lens group G3 is composed of one positive meniscus lens convex onits object side. Three aspheric surfaces are used: one for the imageplane-side surface of the negative meniscus lens in the first lens groupG1, one for the surface nearest to the object side of the triplet lensforming the second lens group G2, and one for the surface nearest to theimage plane-side thereof.

Numerical data on each example are now given. It is noted that thesymbols mentioned hereinafter but not hereinbefore have the followingmeanings:

f: focal length of the whole optical system,

F_(NO): F-number,

2ω: angle of view,

ω: half angle of view,

WE: wide-angle end,

ST: intermediate setting,

TE: telephoto end,

r₁, r₂, . . . : radius of curvature of each lens surface,

d₁, d₂, . . . : spacing between adjacent lens surfaces,

n_(d1), n_(d2), . . . : d-line refractive index of each lens, and

ν_(d1), ν_(d2), . . . : Abbe constant of each lens. Here let x stand foran optical axis provided that the direction of travel of light ispositive, and y stand for a direction orthogonal to the optical axis.Then, aspheric shape is given byx=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y¹⁰ +A ₁₂ y ¹²where r is a paraxial radius of curvature, K is a conical coefficient,and A4, A6, A8, A10 and A12 are the 4^(th)-, 6^(th)-, 8^(th)-, 10^(th)-and 12^(th)-order aspheric coefficients, respectively.

In the following numerical data, length is given in mm.

EXMAPLE 1

r₁ = 73.835 d₁ = 1.20 n_(d1) = 1.80610 ν_(d1) = 40.74 r₂ = 3.773(Aspheric) d₂ = 1.60 r₃ = 6.842 d₃ = 1.70 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 17.434 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.20 r₆ = 4.407(Aspheric) d₆ = 1.80 n_(d3) = 1.74330 ν_(d3) = 49.33 r₇ = −200.000 d₇ =0.80 n_(d4) = 1.80518 ν_(d4) = 25.42 r₈ = 5.242 d₈ = 2.76 n_(d5) =1.48749 ν_(d5) = 70.44 r₉ = −26.974 d₉ = (Variable) (Aspheric) r₁₀ = ∞d₁₀ = 1.30 n_(d6) = 1.51633 ν_(d6) = 64.14 r₁₁ = ∞ d₁₁ = (Variable) r₁₂= ∞(Image plane) Aspherical Coefficients 2nd surface K = −3.269 A₄ =6.23206 × 10⁻³ A₆ = −3.63433 × 10⁻⁴ A₈ = 2.22372 × 10⁻⁵ A₁₀ = −6.62190 ×10⁻⁷ 6th surface K = −3.180 A₄ = 4.24973 × 10⁻³ A₆ = −1.98823 × 10⁻⁴ A₈= 3.04193 × 10⁻⁵ A₁₀ = −2.69865 × 10⁻⁶ 9th surface K = 0.000 A₄ =4.93949 × 10⁻³ A₆ = −1.34150 × 10⁻⁴ A₈ = 1.74837 × 10⁻⁴ A₁₀ = −1.48151 ×10⁻⁵ Zooming Data (∞) WE ST TE f (mm) 5.900 8.200 11.500 F_(NO) 3.624.18 5.00 ω (°) 32.8 24.1 17.5 d₄ 7.29 3.84 1.30 d₉ 6.56 8.37 10.96 d₁₁1.18 1.18 1.18

EXAMPLE 2

r₁ = 31.097 d₁ = 1.20 n_(d1) = 1.80610 ν_(d1) = 40.74 r₂ = 3.332(Aspheric) d₂ = 1.60 r₃ = 6.133 d₃ = 1.70 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 13.488 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.20 r₆ = 4.379(Aspheric) d₆ = 1.80 n_(d3) = 1.74330 ν_(d3) = 49.33 r₇ = 50.000 d₇ =0.84 n_(d4) = 1.80518 ν_(d4) = 25.42 r₈ = 4.563 d₈ = 2.76 n_(d5) =1.48749 ν_(d5) = 70.44 r₉ = −15.315 d₉ = (Variable) (Aspheric) r₁₀ = ∞d₁₀ = 1.30 n_(d6) = 1.51633 ν_(d6) = 64.14 r₁₁ = ∞ d₁₁ = (Variable) r₁₂= ∞(Image plane) Aspherical Coefficients 2nd surface K = −3.146 A₄ =8.64879 × 10⁻³ A₆ = −5.82477 × 10⁻⁴ A₈ = 4.16275 × 10⁻⁵ A₁₀ = −1.37380 ×10⁻⁶ 6th surface K = −3.878 A₄ = 5.28562 × 10⁻³ A₆ = −3.13553 × 10⁻⁴ A₈= 3.29362 × 10⁻⁵ A₁₀ = −2.13641 × 10⁻⁶ 9th surface K = 0.000 A₄ =4.42791 × 10⁻³ A₆ = −4.55843 × 10⁻⁵ A₈ = 1.14056 × 10⁻⁴ A₁₀ = −6.29055 ×10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.920 8.200 11.500 F_(NO) 3.584.16 5.00 ω (°) 32.2 24.0 17.4 d₄ 6.60 3.56 1.30 d₉ 6.76 8.69 11.46 d₁₁1.23 1.22 1.23

EXMAPLE 3

r₁ = 27.175 d₁ = 1.20 n_(d1) = 1.80610 ν_(d1) = 40.74 r₂ = 3.327(Aspheric) d₂ = 1.60 r₃ = 6.087 d₃ = 1.70 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 12.927 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.20 r₆ = 4.355(Aspheric) d₆ = 1.80 n_(d3) = 1.74330 ν_(d3) = 49.33 r₇ = 50.000 d₇ =0.85 n_(d4) = 1.84666 ν_(d4) = 23.78 r₈ = 5.063 d₈ = 2.75 n_(d5) =1.51633 ν_(d5) = 64.14 r₉ = −20.026 d₉ = (Variable) (Aspheric) r₁₀ = ∞d₁₀ = 1.30 n_(d6) = 1.51633 ν_(d6) = 64.14 r₁₁ = ∞ d₁₁ = (Variable) r₁₂= ∞(Image plane) Aspherical Coefficients 2nd surface K = −3.202 A₄ =8.94481 × 10⁻³ A₆ = −6.15065 × 10⁻⁴ A₈ = 4.52314 × 10⁻⁵ A₁₀ = −1.53842 ×10⁻⁶ 6th surface K = −4.132 A₄ = 5.81884 × 10⁻³ A₆ = −4.01777 × 10⁻⁴ A₈= 5.33499 × 10⁻⁵ A₁₀ = −4.58420 × 10⁻⁶ A₁₂ = −1.00000 × 10⁻⁷ 9th surfaceK = 0.000 A₄ = 4.74901 × 10⁻³ A₆ = −8.09534 × 10⁻⁵ A₈ = 1.32302 × 10⁻⁴A₁₀ = −8.52519 × 10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.920 8.20011.500 F_(NO) 3.58 4.16 5.00 ω (°) 32.1 23.9 17.4 d₄ 6.60 3.56 1.30 d₉6.57 8.45 11.18 d₁₁ 1.23 1.22 1.21

EXAMPLE 4

r₁ = 76.650 d₁ = 1.20 n_(d1) = 1.80610 ν_(d1) = 40.92 r₂ = 3.276(Aspheric) d₂ = 1.40 r₃ = 6.251 d₃ = 1.70 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.782 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.20 r₆ = 4.384(Aspheric) d₆ = 2.30 n_(d3) = 1.69350 ν_(d3) = 53.21 r₇ = 300.000 d₇ =0.80 n_(d4) = 1.84666 ν_(d4) = 23.78 r₈ = 6.297 d₈ = 2.40 n_(d5) =1.48749 ν_(d5) = 70.23 r₉ = −13.015 d₉ = (Variable) (Aspheric) r₁₀ = ∞d₁₀ = 1.30 n_(d6) = 1.51633 ν_(d6) = 64.14 r₁₁ = ∞ d₁₁ = (Variable) r₁₂= ∞(Image plane) Aspherical Coefficients 2nd surface K = −1.130 A₄ =1.83732 × 10⁻³ A₆ = −2.30469 × 10⁻⁵ A₈ = 4.01044 × 10⁻⁶ A₁₀ = −1.91354 ×10⁻⁷ 6th surface K = −0.345 A₄ = −5.98870 × 10⁻⁵ A₆ = 6.13929 × 10⁻⁶ A₈= −2.96420 × 10⁻⁶ A₁₀ = 8.00000 × 10⁻⁷ 9th surface K = 0.000 A₄ =4.16180 × 10⁻³ A₆ = 9.37500 × 10⁻⁵ A₈ = 6.17499 × 10⁻⁵ A₁₀ = 1.48794 ×10⁻⁷ Zooming Data (∞) WE ST TE f (mm) 5.923 7.997 11.492 F_(NO) 3.614.16 5.09 ω (°) 32.7 24.8 17.5 d₄ 6.09 3.53 1.30 d₉ 7.10 8.99 12.17 d₁₁1.22 1.21 1.18

EXAMPLE 5

r₁ = 114.165 d₁ = 1.00 n_(d1) = 1.80610 ν_(d1) = 40.92 r₂ = 3.318(Aspheric) d₂ = 1.40 r₃ = 6.530 d₃ = 1.70 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 20.319 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.20 r₆ = 4.040(Aspheric) d₆ = 2.30 n_(d3) = 1.58313 ν_(d3) = 59.38 r₇ = −927.117 d₇ =0.80 n_(d4) = 1.84666 ν_(d4) = 23.78 r₈ = 7.532 d₈ = 2.40 n_(d5) =1.48749 ν_(d5) = 70.23 r₉ = −11.782 d₉ = (Variable) (Aspheric) r₁₀ = ∞d₁₀ = 1.30 n_(d6) = 1.51633 ν_(d6) = 64.14 r₁₁ = ∞ d₁₁ = (Variable) r₁₂= ∞(Image plane) Aspherical Coefficients 2nd surface K = −0.497 A₄ =−5.19094 × 10⁻⁴ A₆ = −8.99866 × 10⁻⁵ A₈ = 3.08269 × 10⁻⁶ A₁₀ = −4.03659× 10⁻¹⁰ 6th surface K = −1.345 A₄ = 1.68161 × 10⁻³ A₆ = 7.65859 × 10⁻⁵A₈ = −9.37869 × 10⁻⁶ A₁₀ = 8.94817 × 10⁻⁷ 9th surface K = 0.000 A₄ =3.57902 × 10⁻³ A₆ = 3.92389 × 10⁻⁴ A₈ = 2.36601 × 10⁻⁶ A₁₀ = 2.89859 ×10⁻⁸ Zooming Data (∞) WE ST TE f (mm) 5.904 7.997 11.498 F_(NO) 3.584.11 5.00 ω (°) 30.5 23.0 16.2 d₄ 6.46 3.68 1.30 d₉ 7.51 9.43 12.66 d₁₁1.20 1.19 1.16

EXAMPLE 6

1r₁ = −125.182 d₁ = 1.00 n_(d1) = 1.80610 ν_(d1) = 40.92 r₂ = 3.312(Aspheric) d₂ = 1.40 r₃ = 7.062 d₃ = 1.70 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 36.331 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.20 r₆ = 4.057(Aspheric) d₆ = 2.30 n_(d3) = 1.58313 ν_(d3) = 59.38 r₇ = 100.000 d₇ =0.80 n_(d4) = 1.84666 ν_(d4) = 23.78 r₈ = 6.615 d₈ = 2.40 n_(d5) =1.48749 ν_(d5) = 70.23 r₉ = −13.364 d₉ = (Variable) (Aspheric) r₁₀ =50.000 d₁₀ = 1.20 n_(d6) = 1.48749 ν_(d6) = 70.23 r₁₁ = −50.000 d₁₁ =(Variable) r₁₂ = ∞ d₁₂ = 1.30 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞d₁₃ = (Variable) r₁₄ = ∞(Image plane) Aspherical Coefficients 2ndsurface K = −0.332 A₄ = −1.50043 × 10⁻³ A₆ = −1.60862 × 10⁻⁴ A₈ =3.25971 × 10⁻⁶ A₁₀ = 6.05120 × 10⁻¹⁰ 6th surface K = −1.287 A₄ = 1.60279× 10⁻³ A₆ = 7.70238 × 10⁻⁵ A₈ = −8.90829 × 10⁻⁶ A₁₀ = 8.95272 × 10⁻⁷ 9thsurface K = 0.000 A₄ = 3.47544 × 10⁻³ A₆ = 4.02997 × 10⁻⁴ A₈ = 3.07449 ×10⁻⁶ A₁₀ = 2.96993 × 10⁻⁸ Zooming Data (∞) WE ST TE f (mm) 5.905 7.99511.496 F_(NO) 3.46 4.01 4.92 ω (°) 31.2 23.6 16.6 d₄ 6.30 3.66 1.30 d₉6.45 8.89 12.18 d₁₁ 0.80 0.80 0.80 d₁₃ 1.32 1.03 1.36

EXAMPLE 7

r₁ = −413.848 d₁ = 1.00 n_(d1) = 1.80610 ν_(d1) = 40.92 r₂ = 3.317(Aspheric) d₂ = 1.48 r₃ = 7.388 d₃ = 1.70 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 43.892 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.20 r₆ = 4.055(Aspheric) d₆ = 2.19 n_(d3) = 1.58313 ν_(d3) = 59.38 r₇ = 100.000 d₇ =1.13 n_(d4) = 1.84666 ν_(d4) = 23.78 r₈ = 6.376 d₈ = 2.43 n_(d5) =1.48749 ν_(d5) = 70.23 r₉ = −15.930 d₉ = (Variable) (Aspheric) r₁₀ =44.301 d₁₀ = 1.20 n_(d6) = 1.48749 ν_(d6) = 70.23 r₁₁ = −44.574 d₁₁ =(Variable) r₁₂ = ∞ d₁₂ = 1.30 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞d₁₃ = (Variable) r₁₄ = ∞(Image plane) Aspherical Coefficients 2ndsurface K = −0.341 A₄ = −1.57613 × 10⁻³ A₆ = −1.57295 × 10⁻⁴ A₈ =3.25595 × 10⁻⁶ A₁₀ = 6.64658 × 10⁻¹⁰ 6th surface K = −1.258 A₄ = 1.50474× 10⁻³ A₆ = 7.67463 × 10⁻⁵ A₈ = −8.90504 × 10⁻⁶ A₁₀ = 8.95276 × 10⁻⁷ 9thsurface K = 0.000 A₄ = 3.48874 × 10⁻³ A₆ = 4.00153 × 10⁻⁴ A₈ = 3.07420 ×10⁻⁶ A₁₀ = 2.96881 × 10⁻⁸ Zooming Data (∞) WE ST TE f (mm) 5.902 7.99411.498 F_(NO) 3.53 4.24 5.00 ω (°) 30.2 22.9 16.3 d₄ 6.20 4.05 1.00 d₉3.46 8.69 8.12 d₁₁ 3.68 0.78 5.04 d₁₃ 1.16 1.23 1.23

EXAMPLE 8

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.362(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.636(Aspheric) d₆ = 4.02 n_(d3) = 1.51635 ν_(d3) = 64.02 r₇ = 30.000 d₇ =1.14 n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = 7.183 d₈ = 1.29 n_(d5) =1.51635 ν_(d5) = 64.02 r₉ = −25.382 d₉ = (Variable) (Aspheric) r₁₀ = ∞d₁₀ = 0.76 n_(d6) = 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞d₁₂ = 0.50 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.37 r₁₄ =∞(Image plane) Aspherical Coefficients 2nd surface K = −0.704 A₄ =2.01910 × 10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀ = −7.41780 ×10⁻¹⁰ 6th surface K = −1.860 A₄ = 1.68779 × 10⁻³ A₆ = 5.98250 × 10⁻⁵ A₈= −9.36385 × 10⁻⁶ A₁₀ = 6.02976 × 10⁻⁷ 9th surface K = −10.683 A₄ =1.92469 × 10⁻³ A₆ = 3.36702 × 10⁻⁴ A₈ = −5.00279 × 10⁻⁵ A₁₀ = 5.80240 ×10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.95 10.08 17.05 F_(NO) 3.15 3.985.39 2ω (°) 64.41 39.67 23.88 d₄ 12.66 5.55 1.37 d₉ 8.97 12.68 18.93

EXAMPLE 9

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.362(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.623(Aspheric) d₆ = 4.23 n_(d3) = 1.51603 ν_(d3) = 64.02 r₇ = 100.000 d₇ =1.09 n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = 8.719 d₈ = 1.13 n_(d5) =1.51603 ν_(d5) = 64.02 r₉ = −25.844 d₉ = (Variable) (Aspheric) r₁₀ = ∞d₁₀ = 0.76 n_(d6) = 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞d₁₂ = 0.50 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.37 r₁₄ =∞(Image plane) Aspherical Coefficients 2nd surface K = −0.704 A₄ =2.01910 × 10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀ = −7.41780 ×10⁻¹⁰ 6th surface K = −3.132 A₄ = 3.33055 × 10⁻³ A₆ = −4.83274 × 10⁻⁵ A₈= −3.28992 × 10⁻⁶ A₁₀ = 4.12519 × 10⁻⁷ 9th surface K = −10.671 A₄ =2.03797 × 10⁻³ A₆ = 3.37686 × 10⁻⁴ A₈ = −4.96072 × 10⁻⁵ A₁₀ = 5.80349 ×10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.95 10.08 17.05 F_(NO) 3.15 3.985.39 2ω (°) 64.40 39.67 23.88 d₄ 12.66 5.55 1.37 d₉ 8.95 12.66 18.92

EXAMPLE 10

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.362(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.607(Aspheric) d₆ = 4.24 n_(d3) = 1.51603 ν_(d3) = 64.02 r₇ = ∞ d₇ = 1.10n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = 9.612 d₈ = 1.13 n_(d5) = 1.51603ν_(d5) = 64.02 r₉ = −26.572 (Aspheric) d₉ = (Variable) r₁₀ = ∞ d₁₀ =0.76 n_(d6) = 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞ d₁₂ =0.50 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.37 r₁₄ = ∞ (Imageplane) Aspherical Coefficients 2nd surface K = −0.704 A₄ = 2.01910 ×10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀ = −7.41780 × 10⁻¹⁰ 6thsurface K = −3.131 A₄ = 3.37249 × 10⁻³ A₆ = −4.66743 × 10⁻⁵ A₈ =−3.92163 × 10⁻⁶ A₁₀ = 4.65697 × 10⁻⁷ 9th surface K = −10.671 A₄ =2.08460 × 10⁻³ A₆ = 3.53565 × 10⁻⁴ A₈ = −5.49632 × 10⁻⁵ A₁₀ = 6.38510 ×10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.95 10.08 17.05 F_(NO) 3.15 3.985.39 2ω (°) 64.40 39.67 23.88 d₄ 12.66 5.55 1.37 d₉ 8.94 12.65 18.91

EXAMPLE 11

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.362(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.603(Aspheric) d₆ = 4.24 n_(d3) = 1.51603 ν_(d3) = 64.02 r₇ = −300.000 d₇ =1.10 n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = 9.954 d₈ = 1.13 n_(d5) =1.51603 ν_(d5) = 64.02 r₉ = −26.804 (Aspheric) d₉ = (Variable) r₁₀ = ∞d₁₀ = 0.76 n_(d6) = 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞d₁₂ = 0.50 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.38 r₁₄ = ∞(Image plane) Aspherical Coefficients 2nd surface K = −0.704 A₄ =2.01910 × 10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀ = −7.41780 ×10⁻¹⁰ 6th surface K = −3.131 A₄ = 3.38882 × 10⁻³ A₆ = −4.78149 × 10⁻⁵ A₈= −3.72655 × 10⁻⁶ A₁₀ = 4.44776 × 10⁻⁷ 9th surface K = −10.671 A₄ =2.10306 × 10⁻³ A₆ = 3.52644 × 10⁻⁴ A₈ = −5.41202 × 10⁻⁵ A₁₀ = 6.22955 ×10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.95 10.08 17.05 F_(NO) 3.15 3.985.39 2ω (°) 64.40 39.67 23.88 d₄ 12.66 5.55 1.37 d₉ 8.93 12.64 18.90

EXAMPLE 12

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.362(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.300(Aspheric) d₆ = 4.31 n_(d3) = 1.51742 ν_(d3) = 52.43 r₇ = −5.152 d₇ =1.20 n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = −20.000 d₈ = 0.95 n_(d5) =1.51603 ν_(d5) = 64.02 r₉ = −24.338 (Aspheric) d₉ = (Variable) r₁₀ = ∞d₁₀ = 0.76 n_(d6) = 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞d₁₂ = 0.50 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.37 r₁₄ = ∞(Image plane) Aspherical Coefficients 2nd surface K = −0.704 A₄ =2.01910 × 10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀ = −7.41780 ×10⁻¹⁰ 6th surface K = −3.112 A₄ = 4.54021 × 10⁻³ A₆ = −8.58413 × 10⁻⁵ A₈= 2.62817 × 10⁻⁶ A₁₀ = 2.91567 × 10⁻⁷ 9th surface K = −10.670 A₄ =2.43162 × 10⁻³ A₆ = 3.02302 × 10⁻⁴ A₈ = −2.43703 × 10⁻⁵ A₁₀ = 3.51356 ×10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.96 10.09 17.05 F_(NO) 3.16 3.985.39 2ω (°) 64.32 39.64 23.89 d₄ 12.66 5.55 1.37 d₉ 8.94 12.66 18.93

EXAMPLE 13

r₁ = 51.401 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.250(Aspheric) d₂ = 2.33 r₃ = 8.280 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.031 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.690(Aspheric) d₆ = 4.00 n_(d3) = 1.51603 ν_(d3) = 64.02 r₇ = 48.276 d₇ =1.09 n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = 8.996 d₈ = 1.13 n_(d5) =1.51603 ν_(d5) = 64.02 r₉ = −32.723 (Aspheric) d₉ = (Variable) r₁₀ = ∞d₁₀ = 0.76 n_(d6) = 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞d₁₂ = 0.50 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.37 r₁₄ = ∞(Image plane) Aspherical Coefficients 2nd surface K = −0.704 A₄ =2.01910 × 10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀ = −7.41780 ×10⁻¹⁰ 6th surface K = −3.132 A₄ = 3.33772 × 10⁻³ A₆ = −4.81743 × 10⁻⁵ A₈= −4.35927 × 10⁻⁶ A₁₀ = 5.17931 × 10⁻⁷ 9th surface K = −10.671 A₄ =2.15229 × 10⁻³ A₆ = 3.18975 × 10⁻⁴ A₈ = −5.59975 × 10⁻⁵ A₁₀ = 6.63410 ×10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.85 10.56 20.05 F_(NO) 3.32 4.396.58 2ω (°) 66.60 38.16 20.40 d₄ 12.66 5.55 1.37 d₉ 9.84 14.64 24.30

EXAMPLE 14

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.450(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.441 d₆= 3.89 n_(d3) = 1.51603 ν_(d3) = 64.02 r₇ = −9.298 d₇ = 0.98 n_(d4) =1.80810 ν_(d4) = 22.76 r₈ = −279.238 d₈ = 0.74 n_(d5) = 1.51603 ν_(d5) =64.02 r₉ = −60.000 (Aspheric) d₉ = (Variable) r₁₀ = ∞ d₁₀ = 0.76 n_(d6)= 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞ d₁₂ = 0.50 n_(d7) =1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.37 r₁₄ = ∞ (Image plane)Aspherical Coefficients 2nd surface K = −0.705 A₂ = −5.57868 × 10⁻³ A₄ =3.37216 × 10⁻⁵ A₆ = 4.60028 × 10⁻⁵ A₈ = −4.71414 × 10⁻⁶ A₁₀ = 1.61550 ×10⁻⁷ 9th surface K = −10.651 A₄ = 3.53185 × 10⁻³ A₆ = 1.08265 × 10⁻⁴ A₈= 2.25584 × 10⁻⁵ A₁₀ = −2.80053 × 10⁻⁸ Zooming Data (∞) WE ST TE f (mm)6.66 10.88 17.35 F_(NO) 3.27 4.06 5.28 2ω (°) 58.61 36.89 23.47 d₄ 12.665.55 1.37 d₉ 9.80 13.25 18.54

EXAMPLE 15

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80400 ν_(d1) = 46.57 r₂ = 4.393(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.567(Aspheric) d₆ = 3.01 n_(d3) = 1.49700 ν_(d3) = 81.54 r₇ = 66.799 d₇ =1.67 n_(d4) = 1.92286 ν_(d4) = 18.90 r₈ = 13.949 d₈ = 1.11 n_(d5) =1.51603 ν_(d5) = 64.02 r₉ = −32.135 (Aspheric) d₉ = (Variable) r₁₀ = ∞d₁₀ = 0.76 n_(d6) = 1.54771 ν_(d6) = 62.84 r₁₁ = ∞ d₁₁ = 0.50 r₁₂ = ∞d₁₂ = 0.50 n_(d7) = 1.51633 ν_(d7) = 64.14 r₁₃ = ∞ d₁₃ = 0.37 r₁₄ = ∞(Image plane) Aspherical Coefficients 2nd surface K = −0.704 A₄ =2.10637 × 10⁻⁴ A₆ = 1.07255 × 10⁻⁶ A₈ = −3.71750 × 10⁻⁸ A₁₀ = 5.72629 ×10⁻⁹ 6th surface K = −3.130 A₄ = 4.08852 × 10⁻³ A₆ = −1.44925 × 10⁻⁴ A₈= 1.73649 × 10⁻⁶ A₁₀ = 7.90457 × 10⁻⁷ 9th surface K = −10.672 A₄ =3.03679 × 10⁻³ A₆ = 1.53844 × 10⁻⁴ A₈ = −7.79567 × 10⁻⁵ A₁₀ = 1.49615 ×10⁻⁵ Zooming Data (∞) WE ST TE f (mm) 5.96 10.00 16.64 F_(NO) 3.13 3.925.24 2ω (°) 64.81 40.07 24.48 d₄ 12.66 5.55 1.37 d₉ 9.50 13.08 18.96

EXAMPLE 16

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.362(Aspheric) d₂= 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) = 23.78r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.538(Aspheric) d₆ = 4.20 n_(d3) = 1.51603 ν_(d3) = 64.02 r₇ = 96.074 d₇ =1.05 n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = 8.579 d₈ = 1.08 n_(d5) =1.51603 ν_(d5) = 64.02 r₉ = −28.441 (Aspheric) d₉ = (Variable) r₁₀ =211.718 d₁₀ = 0.71 n_(d6) = 1.49700 ν_(d6) = 81.54 r₁₁ = 102.523 d₁₁ =(Variable) r₁₂ = ∞ d₁₂ = 0.76 n_(d7) = 1.54771 ν_(d7) = 62.84 r₁₃ = ∞d₁₃ = 0.50 r₁₄ = ∞ d₁₄ = 0.50 n_(d8) = 1.51633 ν_(d8) = 64.14 r₁₅ = ∞d₁₅ = 0.37 r₁₆ = ∞ (Image plane) Aspherical Coefficients 2nd surface K =−0.704 A₄ = 2.01910 × 10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀= −7.41780 × 10⁻¹⁰ 6th surface K = −3.131 A₄ = 3.53969 × 10⁻³ A₆ =−5.76418 × 10⁻⁵ A₈ = −2.28407 × 10⁻⁶ A₁₀ = 3.73706 × 10⁻⁷ 9th surface K= −10.671 A₄ = 2.22302 × 10⁻³ A₆ = 3.59589 × 10⁻⁴ A₈ = −4.93117 × 10⁻⁵A₁₀ = 6.01662 × 10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.95 10.09 17.06F_(NO) 3.16 3.98 5.40 2ω (°) 64.35 39.64 23.87 d₄ 12.66 5.55 1.37 d₉6.05 9.77 16.11 d₁₁ 2.32 2.25 0.37

EXAMPLE 17

r₁ = 37.691 d₁ = 1.20 n_(d1) = 1.80495 ν_(d1) = 40.93 r₂ = 4.362(Aspheric) d₂ = 2.33 r₃ = 8.294 d₃ = 1.62 n_(d2) = 1.84666 ν_(d2) =23.78 r₄ = 16.326 d₄ = (Variable) r₅ = ∞ (Stop) d₅ = −0.26 r₆ = 4.526(Aspheric) d₆ = 4.20 n_(d3) = 1.51603 ν_(d3) = 64.02 r₇ = 92.786 d₇ =1.05 n_(d4) = 1.80810 ν_(d4) = 22.76 r₈ = 8.550 d₈ = 1.08 n_(d5) =1.51603 ν_(d5) = 64.02 r₉ = −30.010 (Aspheric) d₉ = (Variable) r₁₀ =110.638 d₁₀ = 0.76 n_(d6) = 1.49700 ν_(d6) = 81.54 r₁₁ = 123.617 d₁₁ =2.26 r₁₂ = ∞ d₁₂ = 0.76 n_(d7) = 1.54771 ν_(d7) = 62.84 r₁₃ = ∞ d₁₃ =0.50 r₁₄ = ∞ d₁₄ = 0.50 n_(d8) = 1.51633 ν_(d8) = 64.14 r₁₅ = ∞ d₁₅ =0.37 r₁₆ = ∞ (Image plane) Aspherical Coefficients 2nd surface K =−0.704 A₄ = 2.01910 × 10⁻⁴ A₆ = −1.91890 × 10⁻⁷ A₈ = 1.20310 × 10⁻⁸ A₁₀= −7.41780 × 10⁻¹⁰ 6th surface K = −3.131 A₄ = 3.54289 × 10⁻³ A₆ =−4.52245 × 10⁻⁵ A₈ = −4.77798 × 10⁻⁶ A₁₀ = 5.17175 × 10⁻⁷ 9th surface K= −10.671 A₄ = 2.18272 × 10⁻³ A₆ = 4.27937 × 10⁻⁴ A₈ = −6.90882 × 10⁻⁵A₁₀ = 7.84657 × 10⁻⁶ Zooming Data (∞) WE ST TE f (mm) 5.91 10.03 17.04F_(NO) 3.13 3.96 5.39 2ω (°) 64.80 39.84 23.89 d₄ 12.66 5.55 1.37 d₉6.05 9.75 16.03

FIGS. 18 to 34 are aberration diagrams for Examples 1 to 17 uponfocusing on an object point at infinity. In these aberration diagrams,(a), (b) and (c) represent spherical aberrations, astigmatism,distortion and chromatic aberration of magnification at the wide-angleend, in the intermediate setting, and at the telephoto end,respectively, and “FIY” stands for an image height.

Enumerated below are the values of conditions (1) to (6) in Examples 1to 7, from which the modulus sign is removed. Example (1) (2) (3) (4)(5) (6) 1 −25.641 0.31769 45.02 −1.629 1.281 1.949 2 6.410 0.31769 45.02−1.481 1.246 1.942 3 6.410 0.33033 40.36 −1.499 1.231 1.943 4 38.4620.36589 46.45 −1.359 1.228 1.940 5 −118.861 0.36589 46.45 −1.402 1.2811.947 6 12.821 0.36589 46.45 −1.391 1.338 1.947 7 12.821 0.36589 46.45−1.453 1.386 1.948

The values of conditions (11) to (27) in Examples 8 to 17 are givenbelow. Condition Ex. 8 Ex. 9 Ex. 10 (11) 0.92 0.72 0.65 (12) 3.12 3.743.75 (13) 6.47 21.63 INF (14) 0.283 0.337 0.362 (15) 41.26 41.26 41.26(16) 22.76 22.76 22.76 (17) 64.02 64.02 64.02 (18) 1.80810 1.808101.80810 (19) 1.51635 1.51603 1.51603 (20) 0.80 0.82 0.83 (21) 1.29 1.131.13 (22) −0.69 −0.70 −0.70 (23) 3.12 10.39 INF (24) 0.62 0.66 0.66 (25)3.12 10.39 INF (26) 0.75 0.91 1.00 (27) 0.20 0.18 0.17 Condition Ex. 11Ex. 12 (11) 0.62 −0.02 (12) 3.75 4.55 (13) 65.18 1.20 (14) 0.371 0.822(15) 41.26 41.26 (16) 22.76 22.76 (17) 64.02 64.02 (18) 1.80810 1.80810(19) 1.51603 1.51603 (20) 0.83 0.67 (21) 1.13 0.33 (22) −0.71 −0.70 (23)−31.16 −0.54 (24) 0.66 0.67 (25) 31.16 0.54 (26) 1.03 2.08 (27) 0.170.15 Condition Ex. 13 Ex. 14 Ex. 15 (11) 0.71 0.04 0.51 (12) 3.54 5.272.72 (13) 10.29 2.09 14.63 (14) 0.275 4.654 0.434 (15) 41.26 41.26 45.12(16) 22.76 22.76 18.90 (17) 64.02 64.02 64.02 (18) 1.80810 1.808101.92286 (19) 1.51603 1.51603 1.51603 (20) 0.82 0.69 0.81 (21) 1.13 0.311.11 (22) −0.75 −0.86 −0.75 (23) 5.01 −0.97 6.94 (24) 0.64 0.69 0.52(25) 5.01 −0.97 6.94 (26) 0.93 29.00 1.45 (27) 0.18 0.13 0.19 ConditionEx. 16 Ex. 17 (11) 0.70 0.70 (12) 3.91 3.91 (13) 21.17 20.45 (14) 0.0840.069 (15) 41.26 41.26 (16) 22.76 22.76 (17) 64.02 64.02 (18) 1.808101.80810 (19) 1.51603 1.51603 (20) 0.83 0.83 (21) 1.08 1.08 (22) −1.09−1.08 (23) 9.98 9.64 (24) 0.66 0.66 (25) 9.98 9.64 (26) 0.89 0.89 (27)0.17 0.17

The present invention may be applied to electronic taking systemswherein object images formed through zoom lenses are received at imagepickup devices such as CCDs for taking, inter alia, digital cameras orvideo cameras as well as PCs and telephone sets which are typicalinformation processors, in particular, easy-to-carry cellular phones.Given below are some such embodiments.

FIGS. 35, 36 and 37 are conceptual illustrations of a taking opticalsystem 41 for digital cameras, in which the zoom optical system of theinvention is built. FIG. 35 is a front perspective view of the outwardappearance of a digital camera 40, and FIG. 36 is a rear perspectiveview of the same. FIG. 37 is a perspective plan view of the constructionof the digital camera 40. In FIGS. 35 and 37, the taking optical systemis shown as received at a collapsible lens mount. In this embodiment,the digital camera 40 comprises a taking optical system 41 having ataking optical path 42, a finder optical system 43 having a finderoptical path 44, a shutter button 45, a flash 46, a liquid crystaldisplay monitor 47, a focal length change button 41, a mode changeswitch 62 and so on. With the taking optical system 41 received at thecollapsible lens mount, a cover 60 is slid to cover the taking opticalsystem 41, finder optical system 43 and flash 46. With the cover 60opened up to put the camera 40 in a taking mode, the taking opticalsystem 41 comes out of the collapsible lens mount, as shown in FIG. 37.As the shutter 45 mounted on the upper portion of the camera 40 ispressed down, taking takes place through the taking optical system 41,for instance, the zoom optical system of Example 1. An object imageformed by the taking optical system 41 is formed on the image pickupplane of a CCD 49 via a low-pass filter provided with an IR cut coatingand a cover glass. The object image received at CCD 49 is shown as anelectronic image on the liquid crystal monitor 47 via processing means51, which monitor is mounted on the back of the camera. This processingmeans 51 is connected with recording means 52 in which the takenelectronic image could be recorded. It is here noted that the recordingmeans 52 may be provided separately from the processing means 51 or,alternatively, it may be constructed in such a way that images areelectronically recorded and written therein by means of floppy discs,memory cards, MOs or the like. This camera may also be constructed inthe form of a silver halide camera using a silver halide film in placeof CCD 49.

Moreover, a finder objective optical system 53 is located on the finderoptical path 44. The finder objective optical system 53 comprises aplurality of lens groups (three groups in the illustrated embodiment)and two prisms, and provides a zoom optical system with its focal lengthchanging in association with the zoom optical system that is the takingoptical system 41. An object image formed by the finder objectiveoptical system 53 is in turn formed on the field frame 57 of an erectingprism 55 that is an image-erecting member. In the rear of the erectingprism 55 there is located an eyepiece optical system 59 for guiding anerected image into the eyeball E of an observer. It is here noted that acover member 50 is provided on the exit side of the eyepiece opticalsystem 59.

With the thus constructed digital camera 40, it is possible to achievehigh performance and size reductions, because the taking optical system41 is of high performance and small format, and is receivable at acollapsible lens mount.

FIGS. 38, 39 and 40 are illustrative of a personal computer that is oneexample of the information processor in which the zoom optical system ofthe invention is built as an objective optical system. FIG. 38 is afront perspective view of a personal computer 300 with a cover openedup, FIG. 39 is a sectional view of a taking optical system 303 in thepersonal computer 300, and FIG. 40 is a side view of the state of FIG.38. As shown in FIGS. 38, 39 and 40, the personal computer 300 comprisesa keyboard 301 via which an operator enters information therein fromoutside, information processing or recording means (not shown), amonitor 302 on which the information is shown for the operator, and ataking optical system 303 for taking an image of the operator andsurrounding images. For the monitor 302, use could be made of atransmission type liquid crystal display device illuminated by backlight(not shown) from the back surface, a reflection type liquid crystaldisplay device in which light from the front is reflected to showimages, or a CRT display device. While the taking optical system 303 isshown as built in the right upper portion of the monitor 302, it may belocated somewhere around the monitor 302 or keyboard 301.

This taking optical system 303 comprises, on a taking optical path 304,an objective lens 112 comprising the optical zoom optical system of theinvention (roughly sketched) and an image pickup device chip 162 forreceiving an image. These are built in the personal computer 300.

Here an optical low-pass filter F is additionally applied onto the imagepickup device chip 162 to form an integral imaging unit 160, which canbe fitted into the rear end of the lens barrel 113 of the objective lens112 in one-touch operation. Thus, the assembling of the objective lens112 and image pickup device chip 162 is facilitated because of no needof alignment or control of surface-to-surface spacing. The lens barrel113 is provided at its end with a cover glass 114 for protection of theobjective lens 112. It is here noted that driving mechanisms for thezoom lens, etc. contained in the lens barrel 113 are not shown.

An object image received at the image pickup device chip 162 is enteredvia a terminal 166 in the processing means of the personal computer 300,and shown as an electronic image on the monitor 302. As an example, animage 305 taken of the operator is shown in FIG. 38. This image 305could be shown on a personal computer on the other end at a remote placevia suitable processing means and the Internet or telephone line.

FIGS. 41(a), 42(b) and 42(c) are illustrative of a telephone set that isone example of the information processor in which the zoom opticalsystem of the invention is built in the form of a taking optical system,especially a convenient-to-carry cellular phone. FIG. 41(a) and FIG.41(b) are a front and a side view of a cellular phone 400, respectively,and FIG. 42(c) is a sectional view of a taking optical system 405. Asshown in FIGS. 41(a), 41(b) and 41(c), the cellular phone 400 comprisesa microphone 401 for entering the voice of an operator therein asinformation, a speaker 402 for producing the voice of the person on theother end, an input dial 403 via which the operator enters informationtherein, a monitor 404 for displaying an image taken of the operator orthe person on the other end and indicating information such as telephonenumbers, a taking optical system 405, an antenna 406 for transmittingand receiving communication waves, and processing means (not shown) forprocessing image information, communication information, input signals,etc. Here the monitor 404 is a liquid crystal display device. It isnoted that the components are not necessarily arranged as shown.The-taking optical system 405 comprises, on a taking optical path 407,an objective lens 112 comprising the zoom optical system of theinvention and an image pickup device chip 162 for receiving an objectimage. These are built in the cellular phone 400.

Here an optical low-pass filter F is additionally applied onto the imagepickup device chip 162 to form an integral imaging unit 160, which canbe fitted into the rear end of the lens barrel 113 of the objective lens112 in one-touch operation. Thus, the assembling of the objective lens112 and image pickup device chip 162 is facilitated because of no needof alignment or control of surface-to-surface spacing. The lens barrel113 is provided at its end with a cover glass 114 for protection of theobjective lens 112. It is here noted that driving mechanisms for thezoom lens, etc. contained in the lens barrel 113 are not shown.

An object image received at the image pickup device chip 162 is enteredvia a terminal 166 in processing means (not shown), so that the objectimage can be displayed as an electronic image on the monitor 404 and/ora monitor on the other end. The processing means also include a signalprocessing function for converting information about the object imagereceived at the image pickup device chip 162 into transmittable signals,thereby sending the image to the person at the other end.

It is understood that if, in each embodiment, filters such as low-passfilters are removed, the thickness of the camera upon the lensesreceived at a collapsible lens mount can then be much more reduced.

1. An optical system comprising a cemented lens having a cementingsurface on an optical axis of the optical system, wherein air contactsurfaces that are on a light ray entrance side and a light ray exit sideof said cemented lens are aspheric and at least one cementing surface insaid cemented lens satisfies condition (1):6.4<|( r/R)|  (1) where r is a radius of curvature of the cementingsurface on the optical axis and R is a maximum diameter of the cementingsurface.
 2. The optical system according to claim 1, wherein saidcemented lens comprises a plurality of cementing surfaces.
 3. Theoptical system according to claim 2, wherein said cemented lens has onlythree lenses.
 4. The optical system according to claim 1, wherein: saidoptical system is an image-formation optical system that comprises: apositive lens group of positive refracting power which comprises saidcemented lens, a negative lens group of negative power which, uponzooming, is positioned on an object side of said positive lens groupwith a variable spacing interposed therebetween, and an aperture stoplocated between an exit surface of said negative lens group and an exitsurface of said positive lens group.
 5. An optical system comprising, inorder from an object side to an image plane side thereof, a first lensgroup having negative refracting power, and a second lens group havingpositive refracting power which, upon zooming, is positioned nearer tothe image plane side than said first lens group with a variable spacingtherebetween, wherein: said second lens group has only three lenses, alens located in said second lens group and nearest to an image planeside thereof and a lens located on an object side thereof are providedas a cemented lens cemented at a surface on an optical axis of theoptical system, and a d-line refractive index n₂₃ of said lens nearestto said image plane side and a d-line refractive index n₂₂ of the lenscemented to the object side of said lens satisfy condition (2):0.31<|n ₂₂ −n ₂₃|  (2)
 6. The optical system according to claim 5,wherein said three lenses are a positive lens, a negative lens and apositive lens in order from the object side, and a cementing surfacethat is an object-side surface of said positive lens nearest to theimage plane side is a refracting surface of negative refracting power.7. An optical system comprising, in order from an object side to animage plane side thereof, a first lens group having negative refractingpower, and a second lens group having positive refracting power which,upon zooming, is positioned nearer to the image plane side than saidfirst lens group with a variable spacing therebetween, wherein: saidsecond lens group has only three lenses, and a lens located in saidsecond lens group and nearest to an image plane side thereof and a lenslocated on an object side thereof are provided as a cemented lenscemented at a surface on an optical axis of the optical system, and theoptical system comprises an aperture stop interposed between an exitsurface in said first lens group and an entrance surface of saidcemented lens, wherein: a d-line basis Abbe constant ν₂₃ of said lensnearest to the image plane side and a d-line basis Abbe constant n₂₂ ofthe lens cemented to said lens satisfy condition (3):40.3<|ν₂₂−ν₂₃|  (3)
 8. The optical system according to claim 5 or 7,which satisfies conditions (4), (5) and (6):−1.8<f ₁ /f _(w)<−1.2   (4)1.1<f ₂ /f _(w)<1.5   (5)1.7<f _(t) /f _(w)<2.5   (6) where f₁ is a focal length of the firstlens group, f₂ is a focal length of the second lens group, f_(w) is afocal length of the whole optical system at the wide-angle end, andf_(t) is a focal length of the whole optical system at the telephotoend.
 9. The optical system according to claim 5 or 7, wherein at leasthalf of air contact surfaces are aspheric, and in an aspheric shapeapproximated to formula (A), all conical coefficients K are at mostzero:x=(y ² /r)/[1+{1−(K+1)(y/r)²}^(1/2) ]+A ₄ y ⁴ +A ₆ y ⁶ +A ₈ y ⁸ +A ₁₀ y¹⁰   (A) where x is an optical axis provided that a direction of travelof light is positive, y is a direction orthogonal to the optical axis, ris a paraxial radius of curvature, K is a conical coefficient, andA_(4,) A_(6,) A₈ and A₁₀ are the 4^(th)-, 6^(th)-, 8^(th)- and10^(th)-order aspheric coefficients.
 10. The optical system according toclaim 5 or 7, wherein: said first lens group consists of, in order froman object side thereof, a negative lens and a positive lens, two in all,and said second lens group consists of, in order from an object sidethereof, a positive lens, a negative lens and a positive lens, three inall, and said optical system further comprises a third lens groupcomposed of one positive lens, which is located on an image plane sideof said second lens group with a variable spacing therebetween, and is athree-group zoom lens.
 11. The optical system according to claim 5 or 6,wherein: said first lens group consists of, in order of an object sidethereof, a negative lens and a positive lens, two in all, and saidsecond lens group consists of, in order an object side thereof, apositive lens, a negative lens and a positive lens, three in all, andsaid optical system is a two-group zoom lens.
 12. The optical systemaccording to claim 10, wherein: said first lens group consists of, inorder from an object side thereof, a negative lens in which an absolutevalue of a radius of curvature of and image-side surface thereof issmaller than an absolute value of a radius of curvature of anobject-side surface thereof and a positive meniscus lens concave on animage side thereof, two in all, and said second lens group consists of,in order from an object side thereof, a positive lens in which anabsolute value of a radius of curvature of an object-side surfacethereof is smaller than an absolute value of a radius of curvature of animage-side surface thereof, a negative lens in which an absolute valueof a radius of curvature of an image-side surface thereof is smallerthan an absolute value of a radius of curvature of an object-sidesurface thereof and a positive lens in which an absolute value of aradius of curvature of an object-side surface thereof is smaller than anabsolute value of a radius of curvature of an image-side surfacethereof, three in all.
 13. The optical system according to claim 11,wherein: said first lens group consists of, in order from an object sidethereof, a negative lens in which an absolute value of a radius ofcurvature of an image-side surface thereof is smaller than an absolutevalue of a radius of curvature of an object-side surface thereof and apositive meniscus lens concave on its image side, two in all, and saidsecond lens group consists of, in order from its object side, a positivelens in which an absolute value of a radius of curvature of anobject-side surface thereof is smaller than an absolute value of aradius of curvature of an image-side surface thereof, a negative lens inwhich an absolute value of a radius of curvature of an image-sidesurface thereof is smaller than an absolute value of a radius ofcurvature of an object-side surface thereof and a positive lens in whichan absolute value of a radius of curvature of an object-side surfacethereof is smaller than an absolute value of a radius of curvature of animage-side surface thereof, three in all.
 14. The optical systemaccording to claim 12, wherein: an axial spacing between the negativelens and the positive lens in said first lens group is 1.4 mm to 1.6 mminclusive.
 15. The optical system according to claim 13, wherein: anaxial spacing between the negative lens and the positive lens in saidfirst lens group is 1.4 mm to 1.6 mm inclusive.
 16. The optical systemaccording to claim 5 or 7, wherein: said second lens group comprises acemented triplet les having three lenses.
 17. The optical systemaccording to claim 16, wherein: said cemented triplet lens has an axialthickness of up to 6 mm.
 18. The optical system according to claim 17,wherein: said cemented triplet lens has an axial thickness of up to 5.5mm.
 19. The optical system according to claim 16, wherein: the opticalsystem further comprises an aperture stop located right before an objectside of said cemented triplet lens, wherein a ratio of a thickness ofsaid cemented triplet lens to a maximum diameter of said aperture stopis 1.4 or greater.
 20. An imaging system, comprising: the optical systemaccording to claim 5 or 7, and an electronic image pickup device forconverting an optical image formed through said optical system intoelectric signals.
 21. The imaging system according to claim 20, wherein:an angle of incidence of a chief light ray on said image pickup deviceat a maximum image height position at the wide-angle end of said opticalsystem is 15° or greater.
 22. The imaging system according to claim 21,wherein: an angle of incidence of a chief light ray on said image pickupdevice at a maximum image height position at the wide-angle end of saidoptical system is 16° or greater.
 23. An optical system, comprising, inorder from an object side thereof, a first lens group of negativerefracting power, and a second lens group of positive refracting power,and further comprising a cemented lens which has generally positiverefracting power and in which three or more lenses including at leastone negative lens are cemented together, wherein: said optical systemhas a zoom ratio of at least 2, and satisfies conditions (11) and (12):|F _(co) /F _(ci)|<0.95   (11)0.05<D _(co) /D _(ci)<20   (12) where F_(co) is a focal length of thelens located in said cemented lens and nearest to an object sidethereof, F_(ci) is a focal length of the lens located in said cementedlens and nearest to an image plane side thereof, D_(co) is an axialthickness of the lens located in said cemented lens and nearest to theobject side thereof, and D_(ci) is an axial thickness of the lenslocated in said cemented lens and nearest to the image plane sidethereof.
 24. An optical system comprising, in order from an object sidethereof, a first lens group of negative refracting power, and a secondlens group of positive refracting power, wherein: the optical systemcomprises a cemented lens comprising three or more lenses including atleast one negative lens, wherein the cemented lens has generallypositive refracting power, and the optical system has a zoom ratio oftwo or higher, and satisfies condition (13):10<|R ₁ /r ₁|  (13) where r₁ is a radius of curvature of a surfacenearest to an object side of said cemented lens, and R₁ is a radius ofcurvature of a cementing surface located in said cemented lens andnearest to the object side thereof.
 25. An optical system comprising, inorder from an object side thereof, a first lens group of negativerefracting power, and a second lens group of positive refracting power,wherein: the optical system comprises a cemented lens comprising threeor more lenses including at least one negative lens, wherein thecemented lens has generally positive refracting power and an object-sidesurface of said cemented lens is convex, and the optical system has azoom ratio of two or higher, and satisfies condition (14):0.7<|R ₂ /r ₂|  (14) where r₂ is a radius of curvature of a surfacenearest to an image plane side of said cemented lens, and R₂ is a radiusof curvature of a cementing surface located in said cemented lens andnearest to the image plane side thereof.
 26. An optical systemcomprising a cemented lens having a cementing surface on an optical axisof the optical system, wherein lenses that form said cemented lenssatisfy conditions (15) and (16):40<ν_(max)−ν_(min)<80   (15)23.7>ν_(min)   (16) where ν_(max) is the maximum of Abbe constants thatthe lenses in said cemented lens have, and ν_(min) is the minimum ofAbbe constants that the lenses in said cemented lens have.
 27. Anoptical system, comprising a cemented lens having a cementing surface onan optical axis of the optical system, wherein: lenses that form saidcemented lens satisfy conditions (15), (16), (17), (18) and (19):40<ν_(max)−ν_(min)<80   (15)23.7>ν_(min)   (16)60<νmax   (17)1.8<n_(dmax)   (18)1.55>n_(dmin)   (19) where ν_(max) is the maximum of Abbe constants thatthe lenses in said cemented lens have, ν_(min) is the minimum of Abbeconstants that the lenses in said cemented lens have, n_(dmax) is themaximum of refractive indices that the lenses in said cemented lenshave, and n_(dmin) is the minimum of refractive indices that the lensesin said cemented lens have.
 28. The optical system according to claim26, wherein: said optical system comprises a lens group of negativerefracting power, and a lens group of positive refracting power.
 29. Theoptical system according to claim 23 or 26, wherein: at least one of aircontact surfaces on a light ray entrance side and a light ray exit sideof said cemented lens is aspheric.
 30. The optical system according toclaim 23 or 26, wherein: said cemented lens consists only of threelenses.
 31. The optical system according to claim 23 or 26, wherein:said second lens group comprises the cemented lens having, in order froman object side thereof, a first lens of positive refracting power, asecond lens of negative refracting power and a third lens of positiverefracting power, and the cemented lens is a cemented triplet lens. 32.The optical system according to claim 23 or 26, wherein: said secondlens group consist of the triplet lens, wherein said triplet lens is acemented triplet lens.
 33. The optical system according to claim 23 or26, wherein: focusing is carried out by movement of only one lens group.34. The optical system according to claim 23, wherein upon zooming froma wide-angle end to a telephoto end of the optical system, said secondlens group moves monotonously from the image plane side toward theobject side, and said first lens group moves toward the image plane sideand then toward the object side.
 35. The optical system according toclaim 23, which satisfies condition (15):40<ν_(max)−ν_(min)<80   (15) where ν_(max) is the maximum of Abbeconstants that the lenses in said cemented lens have, and ν_(min) is theminimum of Abbe constants that the lenses in said cemented lens have.36. The optical system according to claim 23 or 26, wherein a lenslocated in the cemented lens and nearest to an object side thereof and alens in the cemented lens and nearest to an image plane side thereof areformed of the same vitreous material.
 37. The optical system accordingto claim 23, wherein: an object-side surface of said cemented lens isconvex, and satisfies condition (20):0.50<D _(n1) /Σd<0.95   (20) where D_(n1) is a distance from a surfacelocated in said cemented lens and nearest to an object side thereof to asurface having the largest negative refracting power in said cementedlens, and Σd is a total thickness of said cemented lens.
 38. The opticalsystem according to claim 37, which satisfies condition (21):0.05<D _(n2) /Σd<0.35   (21) where D_(n2) is a distance from a surfacehaving the largest refracting power in said cemented lens to a surfacelocated in said cemented lens and nearest to an image plane sidethereof.
 39. The optical system according to claim 23, wherein: anobject-side surface of said cemented lens is convex, and satisfiescondition (22):−1.5<(r ₁ +r ₂)/(r ₁ −r ₂)<−0.5   (22) where r₁ is a radius of curvatureof a surface nearest to an object side of said cemented lens, and r₂ isa radius of curvature of a surface nearest to an image plane side ofsaid cemented lens.
 40. The optical system according to claim 23,wherein: said cemented lens is convex on an object side thereof, andsaid negative lens is cemented to an image plane side of the lensnearest to an object side thereof, with satisfaction of conditions (23)and (24):−1.0<R ₁ /F ₂<−0.05   (23)0.50<D ₁ /Σd<0.95   (24) where R₁ is a radius of curvature of acementing surface located in said cemented-lens and nearest to an objectside thereof, F₂ is a focal length of said second lens group, D₁ is anaxial thickness of a lens located in said cemented lens and nearest toan object side thereof, and Σd is a total thickness of said cementedlens.
 41. The optical system according to claim 23, wherein: saidcemented lens is convex on an object side thereof, and said negativelens is cemented to a lens located in said cemented lens and nearest toan image plane side thereof, with satisfaction of conditions (25) and(26):2.5<|R ₁ /F ₂|  (25)0.45<R ₂ /F ₂<2.3   (26) where R₁ is a radius of curvature of acementing surface located in said cemented lens and nearest to an objectside thereof, F₂ is a focal length of the second lens group, and R₂ is aradius of curvature of a cementing surface located in said cemented lensand nearest to an image plane side thereof.
 41. The optical systemaccording to claim 40, which satisfies conditions (22) and (27):−1.5<(r ₁ +r ₂)/(r ₁ −r ₂)<−0.5   (22)0.05<D ₃ /Σd<0.30   (27) where r₁ is a radius of curvature of a surfacenearest to an object side of said cemented lens, r₂ is a radius ofcurvature of a surface nearest to an image plane side of said cementedlens, D₃ is an axial thickness of a lens located in said cemented lensand nearest to an image plane side thereof, and Σd is a total thicknessof said cemented lens.
 43. The optical system according to claim 23,which satisfies conditions (15) and (16):40<ν_(max)−ν_(min)<80   (25)23.7>ν_(min)   (16) where ν_(max) is the maximum of Abbe constants thatthe lenses in said cemented lens have, and ν_(min) is the minimum ofAbbe constants that the lenses in said cemented lens have.
 44. Theoptical system according to claim 43, which satisfies conditions (17),(18) and (19):60<νmax   (17)1.8<n_(dmax)     (18)1.55>n_(dmin)   (19) where ν_(max) is the maximum of Abbe constants thatthe lenses in said cemented lens have, n_(dmax) is the maximum ofrefractive indices that the lenses in said cemented lens have, andn_(dmin) is the minimum of refractive indices that the lenses in saidcemented lens have.
 45. The optical system according to claim 26,wherein said cemented lens comprises a positive lens and a negativelens.
 46. The optical system according to claim 23 or 26, wherein saidcemented lens has a double-convex form at or near the optical axis ofthe optical system.
 47. The optical system according to claim 29,wherein said exit-side air contact surface of said cemented lens isaspheric, and said exit-side aspheric surface has an increasingdivergence with distance from a lens center.
 48. An electronic imagingsystem, comprising the optical system according to claim 23 or 26, andan electronic image pickup device for converting an optical image formedthrough said optical system into electric signals.